Tell me something about my body

[MagicNinja]

So I'm walking along and having a good day. I have been drinking lots of water and eating normal good food. I go to the bathroom and suddenly have a headache. I have a headache for the rest of the day.

WTF? I don't understand how my body will suddenly start doing something differently with no catalyst whatsoever. Also, why does the pain feel less if I have a hot bath ? (I know heat relieves pain... why?).

Yea, boring, but tell me random [censored] about why my body feels a certain way, anything, I find this stuff quite interesting.