I felt the same when I woke up.
I blame lack of sleep, lack of caffeine, not enough hydration, and not getting to bed until after midnight.
One Tylenol, bottle of water, cup of coffee, and PB&J later, I am feeling up to starting today's hectic schedule.
Hope you feel better soon.
@grayman just waking again after going back to sleep. I never do that! Try some coffee and see how it goes this time.