I've had a similar thing happen. Basically, if I stay off the caffeine enough to sleep all through the night without waking up, I'll wake up naturally after aro

I've had a similar thing happen. Basically, if I stay off the caffeine enough to sleep all through the night without waking up, I'll wake up naturally after around 7 hours of sleep. At this point I'm still a little foggy and I can easily fall back asleep or lounge in bed for 20min or a few hours. If I do that, like you said, I'll be lethargic. So basically I have to moderate caffeine (for me it is every other day at most and none after 3pm) and get up as soon as I first wake. When I'm very good about no caffeine, regular exercise, and near-perfect diet I require less sleep. Kind of hard to maintain that level of discipline, though. So it's usually 7 hours a night.