It looks like you may be someone who just has looooong cycles. If your highs only lasted for a month or so and the lows for years, I might say differently, but you said you had a least two distinct periods of highs that lasted a couple of years each. So I think for you it's just te way it goes.

I felt the same way except my cycles are very short - two weeks max - but I hadn't been hypomanic since august even when I was off meds for six weeks. But here I am hypo again!