There are products out on the market that claim to tell you how much REM sleep you're getting, but the best way to measure the quality of your sleep is by how you feel the next day. (In fact, fixating too much on your sleep tracker results can work against you, making it harder to get quality shuteye.) Dr. Khosla poses some questions to ask yourself: Do you feel rested upon awakening? Do you nap during the day? Can you do everything you need to do in the course of a day? Of course, everyone has a sleepy day here and there. But if you regularly feel exhausted at any time other than just before bed, it could mean you're lacking in the REM department.