I have sleep apnea, and I haven't been sleeping well the last couple of months - my AHI numbers have been averaging 15 per night, and they should be under 5 (and I would wake up during the night and wake up feeling tired). I finally realized that I needed to readjust the straps on my sleep apnea belt (prevent me from sleeping on my back) - since I did that, my numbers have dropped back below 5.