I think it is just your perception. When you hit your head with the axe, it hurt so much you passed out!

I think that you have a short amount of pain tolerance. Getting hit in the head with an axe hurt so bad that you passed out. I passed out after slamming my head on a fence at full running speed. Barely touching the wall won’t do anything but if you did something like get your finger hit by a rock, you will start feeling really sick and you feel like you’re about to vomit. That is what happens when you have little to no pain tolerance.

This was most likely not very helpful.

When you bump your head, blood goes to the spot where you hit it. If its little, then quite a big amount of blood just wants to get in there. When the bump is big, it has more space for the blood to collect.