How does acupuncture work as an analgesic?

If you've undergone acupuncture, did it work for you? And how well?

• I've had problems with having knots in my shoulders and in general holding my tension in my upper back/shoulders for as long as I can remember. Recently I decided to look into acupuncture to relieve it along with some other things I heard it helps (allergies, PMS, etc.) I'm a skeptic when it comes to even conventional treatment, not to mention alternative treatments. So if you've used acupuncture, successfully or not, to try to treat anything, please let me know what your experience was like and any tips you have for me as someone who has never done it before. Thanks!

• Answer:

  Yes, As a last resort suggestion by my GP for cluster headaches. Maybe 4 treatments, and, I'm a believer! Didn't totally stop the headaches, but the only treatment that ever made a major improvement! Surprisingly, despite the odd nerve being hit while needles were inserted, I found the treatment remarkably pleasant and relaxing