Everyone has different sleeping habits and abilities. I've taken 2 night train trips in recent years. One was on the now-discontinued Elipsos Paris->Madrid train. The other was from Bangkok->Nong Khai (in NE Thailand on the border with Laos). I got little sleep on the Elipsos train. The problem was that we didn't cross into Spain until around midnight, so nearly all of the sleeping time was on Spanish tracks which were much less smooth than French tracks. I was in a 6-person 2nd class compartment. In Thailand I was in a 2-person 1st class compartment but the train was much less modern than European trains. I managed to get a lot more sleep on the Thai train compared to the European train.
When I was young, I took a train from Vancouver to Toronto. After 4+ days on the train, I was quite happy to get off. I didn't have a bed, but I was only 21 years old at the time so I survived. Today I generally can't sleep unless I'm laying down.
Last year a friend & I were on a non-TGV train in France on an extremely hot day on a fully-packed train. A woman came on with her large dog and young daughter. They blocked the aisle with their luggage and their dog. After a short while, the dog got up and crawled under a nearby seat and threw up. The stench was awful. My friend & I were getting off in about 25 minutes, so we got up and waited in the hot area between 2 rail cars to wait for our stop, rather than endure the stench.
Rail strikes are another issue in Europe. I've had train strike problems in France, Italy, and even Belgium. Last year, there was a train strike in France when my friend & I were trying to get back to Paris. There was 1 train running on a day when there normally would have been a dozen from where we were. The ticket office couldn't even sell tickets because of the strike. Instead, we were given a piece of paper saying we were entitled to purchase a ticket on board at the regular price, rather than having to pay a penalty due to boarding without a ticket. The train surprisingly wasn't full, and we never saw a ticket-taker so we got that ride for free.
Twice, including last year, I've had to get to Charles de Gaulle Airport when public transport was on strike. I normally take the RER train. I took a taxi during one strike, and last year, a friend drove us. The woman sitting next to me on my flight missed her original flight earlier in the day due to the transport strike. (RER trains were running, but there was a major slowdown and offloading in some stations, she said.) Air Canada made her pay $300 to take a later flight the same day.