Why no headrush?

Factual Questions
1

After getting out from underneath my house where I had spent the last two hours drilling holes to connect the new refrigerator’s water line, I experienced a pulsating pain in my head for a few minutes. “Headrush,” said my wife. “You were lying down for two hours.”

Fine, makes sense to me, but why don’t I get one after waking up from sleeping for 8 hours?

2

Were your knees bent?

3

Because when you sleep for 8 hours, your body is moving around, changing position, even though you don’t realize it because you’re asleep.

But lying flat on your back in one position for two hours underneath the house, it doesn’t.