I've had this discussion with a few people (including some medical residents) and found that bipolar disorder has become somewhat of a fad, at least in the US. It's the new ADHD. There are many biorhythms that are cyclic, and I think mood is one of them. So, it's very easy to talk yourself into having manic/depressed states. Factor in that there are 4 levels of bipolar disorder and the last 2 feature hypomanic states (not full blown mania) and it becomes extremely easy to come up with a diagnosis of "cyclothymia."
Like you, I find myself preferring the states where I feel like I have energy to burn, but in those times I struggle to sleep properly. Similarly, when I in a more depressed cycle (although, I wouldn't classify it as clinical depression), my appetite goes away, I find it harder to motivate myself to exercise etc. While this technically fits the diagnosis requirements of cyclothymia, I think it's important to remember the cyclic nature of the human body and accept that there will be times of heightened mood and energy and those where those are more depressed.
The standard treatments of bipolar disorder are really unpleasant medications that can carry some nasty side effects. The standard of care for a long time for Bipolar I was lithium. The problem with lithium is that you need to be very careful about salt intake as you can easily become hyponatremic. How you would adequately compensate in someone with CF, I don't know. The others are depakote, lamictal and atypical antidepressants like seroquel.
This is a really good topic. I had a resident suggest that I perhaps had cyclothymia when he learned of my patterns of insomnia coupled with a seemingly high amounts of energy. I followed up with a psychiatrist/sleep medicine specialist who was very informative. I kept a log of sleep/wake patterns, general mood, appetite and energy level. I did find a cycle, and it would technically support a diagnosis of cyclothymia, but I couldn't justify medication.
I wonder how many people with CF are treated needlessly, since it is so easy to support a diagnosis and since we are probably more likely to talk about such things and more conditioned to turn to medication.