Does anyone have experience with REM sleep disorder?

REM Sleep Behavior Disorder (RBD) is a precursor or symptom of Lewy Body Dementia. (Remember that persons may have more than one kind of dementia.) Hallucinations can occur in many kinds of dementia, but they are a hallmark of LBD.

My husband had RBD for a least a decade before the other dementia symptoms showed up. It was very easily controlled by a medication. If he took it he slept peacefully. If he didn't he was punching me in his sleep.

When the dementia was fully evident he needed an additional pill for agitation to help him sleep through the night.

I think many doctors have no idea how hard it is to care for a loved one who doesn't sleep. Those who do understand this do not "wait and see."

If you'd like to see an article about the relationship between RBD and Lewy Body Dementia, Google 
REM sleep problems predict Parkinson's, Lewy body dementia

Of course, your mother may not have RBD. Without an overnight sleep study it would be hard to be sure. If this comes up again, I think I'd insist on a sleep study.

A sleep study can detect RBD. That is treated with a medication. Even if the loved one won't keep a CPAP mask on, knowing whether she has RBD can be useful, so it can be treated.

(I agree with MACinCT: if you won't do the treatment, don't do the test. It is just that RBD has a different treatment than sleep apnea.)