at mine, in a dedicated sleep center, they told me to bring the medications i usually took at night. they "glue" tons of wires to your scalp, and monitors to your chest and everywhere.. you sleep normally for a while and they monitor out of the room via machines you are hooked to and video. then they wake you up if you are having episodes of apnea and try different masks. they tried the little nose mask on me first but i knew strait away it would be pointless cause im a mouth breather and i ended up with a cpap and a full face mask. i stopped breathing 17 times withing an hour of monitoring. pretty severe they said. if you do end up with a machine it takes a little while to adjust but then its not so bad and you actually wake up refreshed for once. major difference in quality of sleep.