Why does my body hate me so?

I was just sitting there, minding my own business, watching TV. Then, I got up to go get a snack, and my leg just collapsed under me. It had gone all numb - kind of like the pins and needles feeling you get when you put a lot of weight on it, and then leave it immobile. Except it was just hanging there, resting on the couch. And the worst part is, it still feels kind of numb, only with periodic shocks of pain going from my ankle to my knee. All I have to say is: What the fuck?