I used to be exactly the same way....particularly my late teens and twenties where I would sleep half the day if I tried to take a nap. Sometime around 40 that

I used to be exactly the same way....particularly my late teens and twenties where I would sleep half the day if I tried to take a nap. Sometime around 40 that changed. I take a nap almost every day, (sometimes 2, esp if doing something mentally taxing...I can do this since I work from home), but it's been years since I have been able to take a nap exceeding 20 minutes. I simply wake up, no alarm or stimuli needed. Even if I was up all night the night before. Sometimes, (like on Sunday afternoon), it's annoying. I would like to be able to enjoy a long nap again occasionally. I've wondered about this, and would love a solid physiological explanation.