Messed up REM or wave cycle. If you're going to nap, you have to time it properly. Naps should be kept between 1.5-2 hours in length so that you get one cycle and are less likely to awaken in the midst of a deep REM or slow wave sleep. Your brain begins dreaming during these periods of sleep so your brain releases a chemical to cause temporary paralysis to avoid injury while dreaming; if you wake up during the middle of that process, you'll be extremely groggy and disoriented -- like you've been drugged. If you only have time for a short nap, no more than 20-25 minutes as you'll typically begin to go into the first stages of deep sleep within 30.
I've had trouble with recurring bouts of insomnia for years so I've read every possible sleep study known to man.
When you wake up you feel really bad, I don't know exactly why, you may feel rested but there's a weird feeling of I don't know, melancholy? Or feeling you've wasted time or something? Or a mix of both and probably more. It's a really weird feeling. Is this what you're talking about?
It's rare, no matter how long I've napped, that I'll wake up delightful and energetic. A few weeks ago I took a little 30 minute nap and felt amazing after it, but I guess it's just a rare, random case.
