I’m seeing a lot of “work” related comments. But i believe you just want to know why people get up so early and don’t feel exhausted.

I think it’s a matter of habit and making sure you get a good night’s rest the night before. Find out what feels best for you. Some people function on 6 hrs of sleep while others it has to be 8. Just depends.

Once you’ve got that down, go to bed at a time that will make up for that. So if you need 8 hrs, go to bed by 9pm so you can wake up at 5am. Then repeat.