I've spent 11 nights on trains in my life, and enjoyed it immensely.
My first nine times were in this country, in the sixties, when I went from Seattle to and from college in NY by train, 3 nights each way (NP North Coast Limited and NYC 20th Century Limited). Back then, on a coach ticket, you could book a $7/night "Slumber coach" roomette. It was half the width of the train (less aisle) and had one chair and a toilet/sink combo. The roomettes were staggered high and low, so each compartment was only about 4' long, with the beds dovetailing. It took two nights to go from Seattle to Chicago. I never had a problem sleeping, but the train kept moving, so there was no lurching.
My only night train experience in Europe was an overnight train from Brussels to Heidelberg in the 80s. It wouldn't have been bad except the train was three hours late into Brussels because it had to wait in Ostende for ferries coming across the stormy channel. I naively thought the train would try to make up the time and set my alarm clock for the scheduled arrival time in Heidelberg, and woke up in Cologne, then couldn't get back to sleep.
My last night train experience was a trip on the Amtrak Zephyr from Reno, NV, to Denver a few years ago. Again, the trip was great, spectacular scenery, and I had no trouble sleeping, but Amtrak seems to think they are running an "attraction" and don't have to be price competitive. The trip was very expensive V-V air travel.
The advantage of night train travel vs air is that you basically use "dead" time to travel. What else are you going to do from, say, 8 PM to 8 AM, except get ready for bed and sleep. If you fly, you have a nights accommodation cost in the first town, get up and prepare to go to the airport, take transportation to the airport, spend the usual time at the airport, going through security waiting to board, boarding, flight time, deplaning, finding transportation into town, traveling into town. then another nights accommodation cost in the next town. So you spend a day and two nights getting somewhere that takes you a night on the train.