This is great advice for people with respiratory and heart problems, but in my experience there are other reasons someone's stupid jerk of a body might not know

This is great advice for people with respiratory and heart problems, but in my experience there are other reasons someone's stupid jerk of a body might not know how to sleep properly. For narcolepsy, circadian rhythm disorders, and other life-ruining sleep disorders that don't have a clear solution, a) a pulse oximeter won't show anything useful, b) if you're in the U.S. your insurance company will fight tooth and nail to keep from paying for a sleep study, and c) a diagnosis is only a small first step towards managing sleep. When you're so sleepy that you can barely function and your doctors can't help very much, it's easy to justify spending a lot of money on any tools that might help.