system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why is it so much harder to fall asleep when you’re thinking about how badly you need to go to sleep?

Yes I need therapy.  Yes I’m working on it 😆
gpt
Going to sleep had two fases. First your body makes a chemical indicating you are going to sleep. It makes you more relaxed and it starts the production of another chemical that will cause the actual sleeping. If you stress, the first chemical won't be produced. That's because if you are stressed your body must be ready to fight off that lion or other danger. The second chemical needs you to be relaxed enough and don't have to much brain activity in your prefrontal cortex.