Brian, My "off/on" can at times actually be a response to lighting situations. No matter how "on" I am, if I were to walk out into the bright sun..........or a red/pink lighting environment, I would be instantly "off". Move me into the shade or turn off the red/pink light and I would be almost immediately (a matter of only seconds) back to the "on" that I had prior to the light. I know it is atypical, but there are those of us out here whose body didn't read the book prior to development of symptoms. I had gradual onset with this problem of a course of several years. (Hind sight is wonderful!) I have not yet spoken with or met a neurologist who begins to offer suggestions/insight or what have you. All I know is that each year the deterioration rate can be marked a little higher. (Grocery stores with pink lighting over the fresh produce are a real challenge for me!). Rita Weeks