Earlier quoted context omitted.
"I’d arrive in a new city each morning feeling refreshed because of the train’s sleeping accommodations." Aeh, where were you travelling? Many countries did not have sleeper trains. Don't get me wrong. I did the same, travelling at night in trains, and it saved me a night in a hotel. But I did not arrive well rested, I arrived train wrecked.
I spent a couple weeks travelling by train across Europe a few years ago on an Interrail pass. I found sleeper cabins were generally pretty comfortable, though you do have to pay extra for them. If you were just sleeping in a seat then yes I can believe you felt awful the next day.
So I go for couchettes. One time in Sweden I found that the sleepers were only 10 euro more than the couchettes, so then I took one.