A temporary disruption of bodily rhythms caused by a not so refreshing nap. You'll find yourself in a state that holds the middle between sleeping and being awake.
Effects such as drowsiness, disorientation, confusion, nausea, feeling crappy and looking particularly cute are not unheard of. To date there is no known cure for nap lag.
Melissa: "hi"
Mark: "hi! how was your power nap?"
Melissa: "not too great, i'm suffering from nap lag.. :("
Mark: "oh noes!1 :O!"
What happens to you when you start nodding offand then you jerk your head back suddenly. Happens a lot when staying on the computer too long. Very dangerous if driving.
If you didn't get enough sleep, and you're driving, please pull over at the first instance of naplash. If possible, get coffee or walk around, or take a proper nap.