I remember hearing somewhere (probably some podcast) that it used to be normal for people to sleep for 3-4 hours, then wake up and do stuff for an hour or so, then go back to sleep for 3-4 hours again. Maybe to help keep watch while you sleep or something similar?
It’s about 50/50 for me. Sometimes getting up and reading for an hour or so will let me fall back to sleep instantly, other times I’m just wide awake at 2AM and then magically get sleepy at 6:30 right before work.
+1 for sleeping without an alarm. If you really need an alarm to get up every day, you might not be getting enough sleep to begin with. Some of that is unavoidable (noises, light waking you up at night etc.) but a lot of people think they can get by with like 6 hours or less of sleep and just get by on extra coffee.
Taking a week or so to just let your body wake up when it wants (even if it means going to bed early, ugh) will help you figure out how much sleep you need.