I did this in 1981 when I first came to Canada aged 23. Not having much money, I couldn’t afford an actual berth, so I had a chair seat that reclined. From Toronto to Edmonton, 2 nights on the train IIRC. Great experience, but nowadays I’d want an real bed!

Did this more recently in 1999 when I was travelling in Europe with my cousin and daughter when we went from Venice to Hamburg. Having had several rather tangled and confusing experiences with Italian trains, we were relieved to find our sleeper train was German, and very clean and efficiently run. We had a 3-berth compartment (3 beds stacked one on top of the other) and I slept like a baby the whole time, the rocking of the train was very soothing.