I often have my foot, or sometimes both feet fall asleep. This goes hand-in-hand with mashing up a tough hill, and lingers for a long time after.

My solution to it, while riding, is to try to get pressure off the pad of my foot by pedaling for awhile with a "pull-up" motion. I avoid pushing down on the pedals at all. This gets the weight off my foot, and gives me a bit of space to then start wiggling my toes. Once the blood is flowing again, the feeling returns to normal.

Sometimes I confuse the numbness with just plain cold.

Having good shoes helps alot. Since I got better fitting shoes, this has been much less of an issue than it was in the past.