sleep inertian.
The grogginess and disorientation that a person feels for a few minutes after a sleep or long nap.
Example Citation:
"'Most people should only nap for 30 minutes or so, ' Camille says. 'More than that and you're getting into deeper sleep.' And the problem with deeper sleep is waking up from it without succumbing to what's known as 'sleep inertia' that groggy, stumbling-around feeling.
James B. Meadow, "Why Z's? Because Workplace Napping Increases Productivity, Authors Say," Denver Rocky Mountain News, November 10, 1999