If you get into bed and fall asleep within 20 minutes, don't remember waking up throughout the night, and wake up feeling refreshed each morning, you should be good to go, Dr. Paruthi says. If not? The best way to find out how much sleep you need is to go to sleep when you feel tired and wake up without an alarm for a few days at time — like when you're on vacation. Then set a bedtime and stick to it for all of the reasons above.