Daze of our lives: This is why you feel groggy when you wake up from an afternoon nap

I hate the way I feel after waking up from an afternoon nap - groggy, grumpy, in a daze, and sometimes even a little down.

This confusing mix of emotions and disorientation was enough to keep me from falling prey to daytime napping for years; I dreaded that feeling, so no matter how tired I was, I fought to stay awake and save my shuteye for when I went to bed at night. 

That said, as I've gotten older, it's been a lot tougher to turn down the idea of a little afternoon recharge.