If you have to catch your breath while falling asleep sometimes, that might be a sign that you will be needing a BiPap. The earlier the better on these, I understand, although I put it off for six months, figuring that the pulmo was just trying to cash in on my ALS. Not so, apparently.
HOWEVER, you don't need a sleep study for a BiPap if you have a diagnosed of ALS.
Sleep studies only identify sleep apnea, a separate thing entirely. But those are doctor's orders, and she went to med school, not me. Actually, this may just be one more example of the Great American Health Care System in action. There was some fussing from the insurance company in paying for my BiPap, because I hadn't had a sleep study that showed apnea (I had two before ALS that showed I DIDN'T). But that is still the diagnosed on my BiPap supplies, "sleep apnea," not ALS.
So, she may just have to game the system and spend unnecessary money on unnecessary tests to get you the equipment you need. I'm (reluctantly) with Glen, because I think it's kind of a rip-off too, but you will eventually need a BiPap, and if this helps you get it, go along. The only problem with sleep studies is getting the gunk out of your hair the next day.
HandinHand ... my FVC was 35% in June, when I started using the BiPap full time, and 46% in September, so this definitely helps. I don't know about oxygen ranges, but certainly ask your pulmo about getting on BiPap asap.