It may very well be AS related. I am not taking enbrel yet (starting next week) and I have had problems with restless legs for years. I have found that what works best for me is to get out of bed, walk around for a few minutes and then stretch. After a few minutes the pain either goes away or is dulled enough that I can sleep. Hope that helps

juggernaut: an unstoppable force or object that crushes everything (AS) in its path