My friend has to go to one for a year. He was hit by a bus. ( I'm actually serious lol), bus hit him, ran over his legs, pants ripped off (lol), hurt his back in the process also... Dude's missing a part of his hind leg muscle and has bad back problems. He laughs about it now. He said he kept saying 'Fuck' every 5 secs when he was in the ambulance. They then loaded his ass up with morphene, then he was all golly and shit. Anyways...
Apperently, they crack your back alot, they give like a massage, at times you'll feel uncomfortable when they're crackin shit, but you feel like a weight has been lifted off your back at the end of the session. Well, that's what he tells me