I have experienced 2 episodes, 4 years apart. The most recent in January this year. While the first was after an extended period of stress, the second was not, and both were actually triggered by physical activity that included bending and pulling. I continue to have days with what I've come to interpret as warning symptoms and have learned to lay low because I can actually start things up if I ignore them. Other days I can do anything I want without a problem. I wonder if anyone else has experienced anything like this?