I've been using a CPAP machine for 30 years. And I have two, incase one quits. But any CPAP machine has to be set for the proper air pressure, and that requires a sleep study. My experience has been that the folks who do the sleep studies keep that information close to the vest so that you have to order a new machine from them.
In my sleep study, they found out that I was waking up about 40 times a night. Not enough to really be conscious, but enough to keep me from ever entering REM sleep, when your body paralyzes so that your body gets real rest. Before my sleep study, I was one who used to nod off for a couple of seconds when behind the wheel and wake up in a different lane, or nod off when I was in a private meeting with my boss. He recognized the symptoms and forced me to see a doctor or lose my job. Saved my life and probably someone else's.