Not sure if you can use this, but here is my experience from a trip from Podgorica (Montenegro) to Beograd (Serbia) in September 2024 (this year). I'm 69 so your experience may differ.
- The copartment had 6 beds - 3 each side. No curtain. I had the top
bed. I tried to avoid this, but booking the day before departure I
had no choice. It turned out not to be so bad, because the room is
extended over the corridor, so I had extra room for my back pack.
- Everybody else in the compartment were already bedded when I
arrived, so there was no question of whether to wait going to sleep.
- I arrived at the station rather early (no plan, this is just how I
am), so I had time to charge my phone before boarding the train.
- I had to go to the toilet 4 times during the night (normal for me).
The toilet at the end of the carriage was broken, so I had to walk
all the way to the end of the next carriage. Next morning I found
that there was another toilet at the other end of my carriage. A
little research would have saved me a lot of walking in a cold
corridor and a VERY cold connection (= the jittery, scrambling,
barely closed walk way betwen the carriages).
- The train was late, so I almost got of at the wrong station, because
it was the next after the scheduled arrival time. Luckily I asked
somebody and found out. At that time I had packed and left my bed. I
wouldn't go back and disturb the other passengers, so I spent 2
hours in the corridor. Next time (if ever) I will check Google maps
BEFORE I get out of bed.
- I didn't try to brush my teeth on the train, but used the station
facilities before and after.
I hadn't travelled in a 6-passenger compartment since the 90s, so this was kind of new.
I still don't know if I will ever do this again, but I am by no means scared of doing it.
Specific for my journey:
The station in Podgorica resembled a Danish province station from the 80s. A dark building and you had to cross the tracks to get to the other platform.
The station i Beograd was light, modern (more modern than Copenhagen Central Station) with a nice restaurant, where I had breakfast, gathered my thought, got som cash from an ATM, and found out which bus to use for my hotel.