I've not tried Reiki, but I use to know a Shen therapist (One of two currently registered in my state). Not the same, but they are related.
I was doing some website work for her, and in exchange I got free Shen therapy. I can tell you it was amazing. The full therapy session had me asleep almost instantly. I woke up feeling as if I'd slept all night, and pain free.
The real kicker came when I had a horrible headache one day. I have neck and back problems, which result in some migraine-like tension headaches. She had me sit on a couch and began her work - again I fell asleep fast (Neither of these times was I the least bit tired/sleepy). A half hour later I woke up on the couch. Again, my pain was completely gone.
None of this lasts forever, of course. But neither does a massage. I've had some great massages in my life and I will testify that I've never felt the relief from a massage that compared to that of Shen.