fear of getting bumped off my plane

Mike, what usually happens if your flight is overbooked (it does happen occasionally) is that the airline puts you on its next available flight (or sometimes a flight of a partner airline) with an available seat. Your old airline, in effect, pays for your new ticket. There are regulations requiring that they pay you a fairly substantial sum (hundreds of dollars) if the replacement flight is more than X hours later than your original arrival time. This has never happened to me, so we'll need for someone else to provide the specifics.

Under normal circumstances it is very helpful to check in for the flight as early as you can and not arrive at the airport at the last minute, though high-status frequent fliers will be the last folks to be bumped.

The scenario you're thinking about--lots of seats kept empty due to COVID-19 when they have already been sold--would be a new situation. I think it's quite unlikely to occur. If it does, it shouldn't be at the last minute, so the affected passengers should be notified ahead of time, not when they arrive at the airport. This sort of thing can happen today when an airline substitutes a smaller plane and there are not enough seats for all the ticketed passengers. The advice in situations like that is to check what other flights are available to your destination--not just on your airline--and figure out your top choices of substitute flights. That makes life easier for the airline employee who assists you with the necessary rebooking, and it allows you some control over your new departure time, the connecting time on the new itinerary (if any), etc. You won't necessarily get your top choice, but being prepared with that information may allow you to avoid the really unattractive options.

But it's not likely to happen.

I have been on a Virgin flight from London to San Francisco several years ago that was overbooked. Someone was moving down the line asking for volunteers to be bumped off. You were put up in a hotel for the night, all meals paid for, compensation and a free Virgin flight, so many took them up on this offer.

Your airline won’t let you get to the airport before they decide to keep middle seats empty.

You can look at any statistics to know that the virus is serious. Older people and overweight diabetics seem to be more at risk, but many healthy people your age have succumbed, including children. Hostels will presumably be operating with social distancing in place.

Stressful to imagine all sorts of scenerios, but June is too early to guess what might happen in October. This is all new to everyone, so wait and see.
My national airline is returning to every seat booked before September. Others may be similar.
You have been given the situation of overbooked flights. Some things to reduce stress is ensure you are signed up to receive flight changes by email....or download their app. Because emails are not 100% guaranteed, check your booking number on their website once a month and then the week before your flight. You can check in on line 24 hours prior to take off...do this!!! Personally, at least on a long haul or infrequent flight, I pay for a seat early. You might feel better prepurchasing an aisle or window seat so you know you have a seat.
You can adjust to any travel situation. Ensure you have a little more money in the budget, and be sure to not arrival late at night at the hostel in case they hsve filled beds. I also would email or call a few days before to reconfirm your booking. Ensuring you are on their radar helps.
The one thing you cannot control is any restriction on flights. You may not be alallowed to fly to Spain on a US passport for tourism only....or you may be required to quarantine. You won't know about flight restrictions for October at this point. It might help to jave some idea how to quarantine in unknown territory or if that will be a deal breaker.
I hope your lodgings were not booked 'non refundable'. Restrictions are still too uncertain to be that confident.

When overbooked, the first thing an airline does is ask for volunteers to bump. They usually offer a new flight and compensation. (If you have the time to reschedule, you can sometimes negotiate a great deal.)

If not enough volunteers, they start bumping. There is a hierarchy as to who is bumped first. Usually those on the cheapest fares and purchased from a third party are first to go. (No loyalty to the airline.)

One tip I was told by an airline employee was to join that airline's frequent flyer program. It doesn't cost anything and the airline doesn't want to risk alienating you even if you are new. You might be a frequent flier who is changing allegience to their airline. They don't know. Make sure your FF account number is on your reservation. I belong to almost all of them. Even if I am taking an airline once and probably won't fly them again I join.

If you are bumped, they will do their best to get you on the next available flight. If flying to Europe or back, you will probably also get some compensation.

As stated earlier, the airline won't suddently decide to block middle seats. This will be done days in advance and you will be notified. They will notify you about a change to your flight. Usually with a suggested alternative.

I doesn't matter if you've had coronavirus or not. Of course, if they are checking temperatures at the airport, and yours is high, you will probably be denied boarding.

Being bumped has always affected a small sliver of passengers, and they have the right to get compensated for it. In recent years, there has been additional pressure or airlines to minimize this practice and, frankly, there does not appear to be a real problem if you look at the statistics. I accepted quite a nice sum once for taking a later (domestic) flight, that's probably the worst that can happen. I'm not sure I would worry about this relative non-issue in comparison to not even knowing if you'll be allowed entry in the first place, and staying in a potentially crowded hostel. Since a lot of things in hostels are shared, I'd want to know how they'll deal with common areas, shared utensils, etc. It's likely that the hostel business model as we knew it prior to COVID will not be the same. This may make it less attractive to stay in one, depending on what parts of the hostel experience were most important to you.

In a real, fair, and logical world there would be a simple solution to forced rebooking. If after all inducements there are still too many passengers, then the last passengers to have booked their tickets are those forced off. No matter who they booked with, or their airline status , or other self-importance. In all fairness priority must be given to those who made plans first. If you booked your seat before every seat was sold, you should never be forced off. And the booking engines should show at that point that all seats are currently booked and you will be allowed to fly on that flight only if there are cancellations. I suppose this is too easy and too-anti-airline.

One the flip side, if the flight is overbooked and you don’t mind being bumped and hanging around the airport for a few hours (or more), you can get a nice little airline (or maybe cash?) credit. Last time flying via Montreal, they were looking for volunteers and it started around $500 and went up to around $1500-2000...I tell ya, I was so tempted, but just wanted to get home after flying from overseas.

As has been noted, it is likely you would know ahead of time about a seat assignment change due to reduced capacity. Most airlines have been pretty generous on rebooking (at least Delta was, for me). I also hope you have refundable reservations for your hostels, etc. Having just gone through canceling my June trip, I learned a hard lesson about making flexible/refundable arrangements.

I would be more concerned about being allowed into the country at all, which you're not going to know for several months. Keep an eye on the US State Department page for Spain, particularly the travel advisory and alert sections. The alert posted there yesterday says this:

Spain: Transportation options and border restrictions continue to
change throughout Europe. U.S. citizens are allowed to depart the
European Schengen area, including Spain. However, only citizens or
legal residents of the European Schengen zone are allowed to enter the
European Schengen zone. Spain’s air, land and sea borders will reopen
to other EU countries gradually after June 21. Land borders with
Portugal will open on July 1. U.S. citizens without
Spanish/EU/Schengen citizenship/residency likely will be barred from
entering or transiting Spain by air, land, and sea. Please consult
with the closest Spanish Embassy or consulate about your specific
situation before making travel plans to Spain. More information on
European border restrictions is available here.

I hope things work out for you.

I worked one time for Virgin Atlantic. at O'hare Chicago to London flights,
Whenever we overbooked (usually in the summer) we had a plan of options in place to offer passengers to get everyone on a flight.
We sent some to our rivals at British Airways and other airlines and they would do the same when faced with similar situation
We knew that there was a certain kind of experienced passenger that would jump at the options.
For example we had a stag party of guys one time that opted to stay in Chicago another day as long as we payed for the hotel and an upgrade to premium class on the flight the next day

Do what I did in the past. Tell them you know Lefty Baumgartner. Guaranteed seat. They will remove some old biddy in line instead.

These are all very wise suggestions and comments.

Years ago, before 9/11, my husband, child and I were all bumped off a flight. Our checked bags had gone ahead. The airlines paid for our hotel and meal which was great, but we had no nightwear, slippers, meds, toiletries, change of clothes. Dumb, but we learned. In the current situation which seems to change daily if not hourly, being extra prepared is the way to go. Also having extra food, snacks and filled water bottle in your carryon is highly recommended from personal experience being stuck in the airport when everything's closed.

Good luck and hope you will travel safely and smoothly.

As Frank notes, the passengers with the lowest cost airfares are the first to be bumped. The logic is involuntary denied boarding (cash, not a voucher) compensation is based on the price of the ticket.

Passengers who are denied boarding involuntarily due to oversales are
entitled to compensation that is based on the price of their ticket,
the length of time that they are delayed in getting to their
destination because of being denied boarding, and whether their flight
is a domestic flight or an international flight leaving from the
United States. This is called “denied boarding compensation” or “DBC”
for short.

Most bumped passengers who experience short delays on
flights will receive compensation equal to double the one-way price of
the flight they were bumped from, up to $675. Passengers experiencing
longer delays on flights will receive payments of four times the
one-way value of the flight they were bumped from, up to $1,350.

https://www.transportation.gov/individuals/aviation-consumer-protection/bumping-oversales#

Thanks for your input.
I do have a frequent flyer number for American Airline.

How serious or unserious Coronavirus disease is or my chances of catching the virus, would be unknowable; some will insist that it is so serious, I shouldn't take even the tinyest chance of catching it. Other opinions say, my chances of catching it are low, my chances of having symptoms if I catch it are low, and so on. Others may have discussed this in other threads. I am skinny, with no diabetes or known major health problems. It is tempting to just cancel my trip now to avoid feeling too guilty of stupid for doing something my mother doesn't want me to do, or for feeling like an ornery kid doing something that is supposed to be too dangerous. If the travel industry is open, the plans are going to operate, there are no quarantining rules entering Spain or returning to the USA, , the sites are open, my logging places are open and letting me continue with sleeping there, and so on, then I will continue with my trip. As of now, I thought i read that travelers are only allowed to return to the USA arriving at certain airports. My flight is scheduled to return to Philadelphia, which isn't one of the listed airports. My mother read an article recommending not to sit in a middle sear; she has had a lifelong phobia of travel, she has never ridden in a plane. I do put a mask on (properly, not like some who keep it under their chin, or over their mouth but not covering their nose) before every time I step outside my apartment. In case I show up at the airport and am denied boarding, that could be at the minimum $75 wasted on the taxi.

My mother doesn't know about my plans. Maybe I will travel without telling her. I live alone now.

My original reason for staying in hostels was to increase my chances of having minimal conversation with other English speakers, given that I am actually traveling alone. I try to remain unintrusive. I don't put a lot of effort into trying to talk to people. I am open to conversing a little if somebody wants to. If I am on my way somewhere and somebody wants to talk, I'll end the conversation after a few polite sentences. Saving money is just a side effect or coincidence, although my budget is still low compared to some (typically older) wealthy travelers who may not consider staying at any place that isn't a four or 5 star hotel.

Edit: my hostels and one hotel room are refundable until 1 to 2 weeks in advance.

Dude I am 51 now I stayed in hostels in my 40's usually the oldest person

One tip I was told by an airline employee was to join that airline's frequent flyer program. It doesn't cost anything and the airline doesn't want to risk alienating you even if you are new.

My wife is silver status with BA and has been bumped on several occasions. She flies weekly for work so her exposure to the risk of being bumped is subtantially higher than the average flier.

As a family we've been on a number of flights that have been overbooked (I think it's more widely practiced than many people think it is), the ground staff have always asked for volunteers accompanied by a few incentives. If there are no takers then people will be told that they are being denied boarding. Our experience is that they don't do this to families with young children. There's clearly some hierachy in terms of who gets denied but having FF status with the airline isn't guaranteed to provide immunity.

JC, I agree. British Airways is in a class unto themselves. I think they so want to be a discount airline that the ground personnel could not care less about people sitting in upper classes or those with frequent flier status.

Everyone is treated like garbage.

In my experience, flight crews are good.

there does not appear to be a real problem if you look at the statistics.

That's probably true, especially if you compare it to the past. We haven't been bumped in decades. I think the last time was returning from Paris over 20 years ago. But I do remember one trip to France where I was certain we were going to be bumped. We were flying through Kennedy in NY, and when we got near the gate we heard that they had overbooked by something like 175 people. And I heard someone saying that he had been coming to the airport for the last 3 or 4 days in hopes of getting on the plane. I still never figured out how, given those figures, we managed to get on the flight.

Mike L. I wouldn't worry about bumping. A change in schedule between now and then is more likely. The way to prepare for the slight possibility that you would be bumped, is to know your rights for compensation, and have a contingency plan for what you'd do.

The last time I was on an overbooked overseas flight, the gate agents asked for volunteers to give up their seats in exchange for a guaranteed seat on the next flight, and a voucher for future flights. They kept raising the amount of the voucher until they got enough volunteers. I think it was up to $800, so some people with the flexibility to wait a day made out very well.

After the case of Dr. David Dao being bumped and physically dragged of the plane, airlines are going to extremes to have passengers volunteer to get off the plane. Chance of an involuntary bumping should be small.

A number of years ago during my business travel days, a passenger near me jumped up when the flight attendant requested volunteers to give up their seats. As he gathered his carry-on bags he said that this was his third voluntary bump. For the right price, someone will voluntarily give up their seat.