I've not tried reiki, but I have a scoliosis which makes sciatica an unwelcome guest in my life on a regular basis. I've tried all sorts of alternatives, but good old physiotherapy and associated exercises keep me mobile. I felt an unwelcome twinge a couple of days ago so will keep the physio's number handy. I hope that others on this post may be able to offer alternatives.
If it's your first attack try a hot-water bottle and immobility for a while. It used to ease it for me. The cause is important so it would be a good idea to discuss it with your doctor.