system
Given the following post, respond as if you're commenting on Reddit:
human
Why do I feel more tired after 11-12 hours sleep than after 7-8 hours sleep?
gpt
Here's the real answer: your body goes through many sleep cycles, each lasting about 90 minutes. If you sleep for 7.5 hours (5 cycles) you will feel a lot better than if you sleep for 8 hours (in the middle of your sixth sleep cycle) even though you are technically getting more sleep. When you sleep later, you tend to be woken up (by light, sound, etc) in the middle of a sleep cycle, which causes you to feel tired. You should set your alarm so that you wake up at the end of a sleep cycle, accounting for how long it takes for you to fall asleep (around 14-30 minutes on average.) There are websites that will calculate when you should set your alarm so that you'll wake up at the end of a cycle.