These two replies seem to correlate with my thinking.

I know exactly what you mean and I've asked myself the same question before. There can indeed be changes within an episode (hypomanic, manic, depressed) but I wouldn't say these are cycles within a cycle, per se. It would perhaps be more appropriate to describe them as fluctuations rather than cycles - you can fluctuate between varying levels of severity during an episode/cycle.

Think of it as the way anybody's mood fluctuates and changes to a varying degree, but within an episode for someone with Bipolar Disorder it's contained within the current ruling "state".

So it's not really cycling within a cycle, its just the varying levels of severity of the episode which can be interpreted as fluctuating changes in overall mood.