Had one for knee surgery about 6 years ago. It wasn't bad, but I had the side effect called "spinal headache." The hole from the needle going into my spinal column didn't close on its own, so whenever I would sit up I would be internally losing a small amount of spinal fluid from my spinal column. It caused a massive headache and dizziness because the small leak was actually causing my brain to "sag" a little bit. They fixed it by taking a small amount of blood and injecting it into my spine. The blood coagulated and closed the hole, which instantly (and I mean instantly) alleviated the dizziness and headache.
I forget what the chances of spinal headache are, but I wouldn't worry too much about it. Just know that it'* a possible side effect and could cause discomfort if it happens. Easy to fix, though