[DSMan195276]

That's not entire true. Getting a full sleep cycle is important - More over, the reason you don't feel groggy after sleeping for 20 minutes is because you didn't actually enter into the deeper levels of sleep, which are important for actually being rested.

If you sleep for aprox. 90 minutes, a full sleep cycle, then you also won't feel groggy.

[albemuth]

Isn't the theory around the uberman that in those 20 min you go straight into deep sleep?

[baby]

yup, parent is talking without knowledge of uberman

[bryanlarsen]

I still feel groggy after a 90 minute sleep; it's not as bad as waking up in the middle of the cycle, but I still feel groggy. If I nap for 3-15 minutes, I wake up feeling as awake as I am during exercise.

[bsummer4]

Are you sure you're not still waking up in the middle of the cycle? 90 minutes is just a loose generalization. Different people have different sleep cycles and take different amounts of time to fall asleep.

Personally, 2 hours works well for me but 90 minutes does not.