Why, when my leg/arm/any limb “goes to sleep” does it hurt once the feeling starts coming back to, but if I am given a numbing agent, it doesn’t hurt when the feeling comes back?

Question

So, when you fall asleep leaning on your arm and roll over, it starts to hurt as the feeling comes back. But if you go to the dentist and they numb your mouth, it doesn’t hurt once that starts coming back?

In: Biology

Answer 1

The feeling you are describing (often called pins and needles) is the result of a reduced blood flow. Your body weight basically cut off the circulation to some degree. I can’t tell you exactly why it is uncomfortable when it starts to move properly again. Maybe someone else can chime in on that.

A numbing agent dampens the nervous signals, but doesn’t mess with the circulation in the same way.

Edit: some good answers came in while I was typing, refer to those for a better explanation of the why