They hurt, but it's not like a 'crack your head open' kind of hurt. They're tinkering around with your spine, so it's more like a nervy kind of pain, like if you eat something really cold, and it hurts one of your teeth.
I never knew about the laying flat on your back thing. When I had mine, they were trying to rule out meningitis. I had to stay in the hospital room for a few hours, but I think that was mostly because they gave me morphine.
I hope you're recouping well!