"sleeper train" is the key here. Another keyword to search for is "couchette", I think that's how it's called in some places. See e.g. https://en.wikipedia.org/wiki/Couchette_car and the map.
Both times I'd say well rested would be a stretch. The first time felt a bit like a magic carpet in that I got somewhere while using up no useful hours but it still wasn't perfect.
I suppose it’s the novelty of sleeping in a moving vehicle, my flight attendant friend said it took them a while to start sleeping well on long haul flights.
Perhaps with a lot of benzodiazepines or drowsy anti-histamines I could attempt to sleep well in a sleeper train, but not normally. Happy for those who can of course.
Do you think it's the noise for you, the movement, or something else (like lack of privacy)? I started taking earplugs with me for any kind of trip now, they are a godsend.
Most sleepers also offer cabins with proper beds (for a premium).