I used the Ab Circle Pro for 2 days and couldn't use it the third day because I was in sever pain! The pain I have is going all the way from the top of my neck and down the right side of my back. I also was not able to use or lift my left arm for several days due to the extreme pain! It still hurts to turn my head to the right or the left and I hear a cracking sound when I try to do so. I have never in my entire life had anything like this happen to me. I can't even get a good night of sleep because of the pain, it's impossible... read full review »