I have lost count of the number of times I have gone of meds... (my pdoc says its about the same number as he as gone of his migrane meds!) I think the longest I have lasted without mania is about a month, and the longest off meds about 2 months...
All the best, I guess it depends on whats happening in your head, how much you can change what you think and feel...
My guess that exercise, diet and sleep are the keys... maybe I should listen to my own advice