I'm on my 5th machine first 3 machines were cpap now on Bi-pap I qualify because of my O2 in the blood level drops less than 68% ... I stop breathing for long periods of time I guess.. i find the Bi-pap is more comfort to sleep with.. I have have 3 sleep studys and they want to do another and another thung I use to do was sleep driving.. even while I was using the machines, there a stay awake pill they put me on is provigil