I don't know what causes it. I have experienced the same. I have hep c and a side effect of hep c, fibromyalgia. I work on my feet so it can be quite a challenge. I have been taking Elavil at nite and it has really helped my chronic pain. Also, I increased my water intake, reduced the caffeine and try to pace myself (actually I live to work, don't get much else done). Let me know if you find anythin that helps you. I had the stingy needle burning feet and ankles as well several years ago.