I’ve done that route Portland to Chicago twice, with a CPAP both times, and never even woke up. I also use a full mask. I really don’t think you’ll have any problem.
I use a Philips Dreamstation Bipap. Its very similar to CPAP.
I keep mine on the nightstand. My bed is about a foot higher. Sometimes I wake up and hear gurgling in the tube. No big deal. I take off the mask and hold down near the floor. The water clears quickly and I put the mask back on.
Water is optional. I often use mine without water. Depends on the humidity and how dry my nose feels.
I skip the water if I’m traveling. Carrying a gallon of distilled water is too much hassle.
My machine has a heat function. I’ve never used it because my room is warm. Heating water would encourage mold.
In that case, it happens in Spokane when the trains from Portland and Seattle meet up. If both trains are running on time it’ll be shortly after midnight, but delays are common on Amtrak so it could happen at any point in the night. The sleeper car attendant goes off duty from 10 PM to around 6 AM (they have to sleep too, after all) but your friend should be able to ask them before they turn in if they’re expecting to make Spokane on schedule.
Or if you have a cell connection (you should), you can go here, which gives a fairly up-to-date status.
The only other suggestion I can make would be to use double-sided foam tape (making sure you get the kind that removes without residue) to keep the unit in place. The little extra thickness can make a lot of difference.
Thanks again for all your hints and suggestions. I have shared them, so hopefully he’s a bit less worried about it.
If your friend is getting on the train in Spokane heading east, the changeover/combining trains with any possible electricity power gap will have happened in Spokane by the time they board and get shown to their sleeping compartment. From there to Chicago it’s unlikely any more power interruption unless there is a mechanical breakdown or major weather event.
If they are continuing on east from Chicago on any number of Amtrak eastern region trains, a Amtraks disability assistance service specialist recently told me that electrical power supply gaps are far more likely to happen than from the west to Chicago. Older rolling stock, more stops, more junctions where something can go wrong. I was asking about my oxygen concentrator because its battery can cover slightly less than 3 hours without needing to be plugged in.
Overall, train travel is vastly easier than trying to fly with medical devices and I found Amtrak staff incredibly helpful compared with airports or airlines.