just had this done on me the other night, and all i can say is wow.
went for a massage to deal with this funky kink i still have in my sacroiliac region. because it's quite sore, the massage therapist opted to do cranial sacral work instead.
to be honest, i don't know all the particulars, but the technique [which admittedly sounds a bit new agey] deals with the diagnosis and 'energetic' manipulation of some brain or spine fluid, or some such thing. this fluid supposedly has a rhythm of its own that can be felt and re-routed, so to speak.
i don't know how it works, but all i can say is i never felt such deep relaxation. in fact, i totally nodded out a few times. it's like getting a vulcan death grip minus the pain of a squeeze. the thing is, there is barely any pressure applied to the area. it reminds me a little of reiki, but i've had reiki done and never really felt anything. usually i'm more down for a serious deep tissue massage, super firm pressure, almost to the point of pain. with cranio sacral, there was the lightest pressure, then i would feel a wave of something going through me, and then i'd nod out. it was a trip.
my back isn't 100% healed, but i did feel something softly pop into alignment today, in both the lower back and upper right shoulder, where she also did a bit of work.
pretty amazing stuff. try it if you get the chance.
http://www.altguide.com/therapy/info/cranio.html