I haven't used an alarm clock in 20 years and wake up within the same 5-10 minute window almost every day.

I have a friend that will just sleep through multiple alarms. But he can also just fall asleep in 10 minutes on an airplane and I can't sleep at all on a plane. He also takes lots of naps and I never take a nap unless I'm sick.

The worst feeling to me is waking up from some external noise. I just feel so groggy afterword. My body will feel better after 5 hours of sleep and I just wake up naturally compared to 5 hours, go back to sleep for 2 hours, and get woken up during the wrong time (middle of REM cycle?) and then I feel tired for the whole day even though I got more sleep.