This daytime sleep study measures how sleepy you are. The test is usually done immediately after an overnight study. A series of five naps are taken at two-hour intervals. This is done because your ability to fall asleep changes throughout the day. During this test the technician records whether you fall asleep during the test and whether you go into rapid eye movement (REM) sleep during the naps. This test is used to diagnose sleep disorders such as narcolepsy and idiopathic hypersomnia.