im in my mid 30s and have been the same since I was ~12 years old. I finally figured out why in the past year since having a good sleep tracker: 75% of my rem sleep happens between 5:30am and 8:30am. I go to bed around 12:00 and sleep until 8:30am usually. if I have to get up before 8:30 i frequently feel totally out of it and exhausted for a while, now I'm thinking because thats frequently being woken up directly from REM sleep.