Deep sleep is a period of sleep when your brain waves are at their lowest frequency. This is when it is hardest to wake you up. Usually, people get spurts of it within the first couple of hours of the night. Some with genetic mutations are able to get more deep sleep, but studies are showing that around 20% of deep sleep for adults is optimal. This equates to around 1.5 hours a night or more. You can track deep sleep through tracking devices such as an Oura ring, Fitbit, Whoop, and other brands. You may be able to tell if you’re not getting enough deep sleep if you’re waking up a lot early on in the night, not feeling rested in the mornings, even with 8+ hours of consistent sleep every night.