I'll admit, six years ago when I was diagnosed with rapid cycling cyclothymia, I hadn't heard of it. And I minored in psychology. The last time I visited a new (non-psychology based) doctor and had to list pre-existing conditions, their system couldn't find it and I had to manually type the name into the computer myself, because the nurses had never heard of it. I had to then explain what it was, and still got bemused looks.
When you google cyclothymia, half of the resources call it "mild". Perhaps when compared to some other cycling conditions, including the full manic episodes and long-lasting depression of Bipolar I and II, it is mild. But rapid cycles between depression and hypomania, and the anxiety that goes along with it, is by no mean mild compared to, say, life without those. In mentions of mental health conditions, cyclothymia is rarely included in the list. In searching for resources, it seems impossible to find anything that's not a medical source - nobody blogging or writing about it. There are few personal sites or forums dedicated to it. I have found no organization that focus specifically on it. In addition to cyclothymia being elusive, rapid cycling is particularly rare, as is having more hypomania than depression (it's usually the reverse). Because of this, my medication, which is prescribed to help my hypomania and does not directly affect depression, is not as frequently prescribed for cycling. Which means that finding resources on my medication with the primary usage being cyclothymia, or any type of mood cycling, isn't particularly easy. (The primary usage is for seizures). And finding personal resources, information from others on my same medication for rapid cycling cyclothymia, seems downright impossible.
It's a lonely feeling. When people question that your condition is real, try to placate it with silly patronizing "advice", stigmatize you, to have such a difficult time providing legitimate resources, or finding health professionals that have even heard of it, is incredibly isolating. I know that I'm not alone in this. I have friends and relatives with equally rare, if not more rare, conditions, and they too have to explain their illness at length, say "yes, I promise, this is a real thing". They too have people question that it's not "all in their heads". They too have to deal with assumptions and misconceptions. They too have to explain that they always have a condition, that they're always battling, even when you can't visibly see it.
I've been lucky enough, in my focus on mental health support and advocacy, the "meet" (virtually) others who have cyclothymia, and a few others who have rapid cycling. I say lucky not because I'm glad that anyone else has it, but because at least if we have to have it, we have the opportunity to build a support network for each other. And because I do experience symptoms of other mental health conditions, such as Major Depression, Bipolar Disorder, and Generalized Anxiety Disorder, I have met many amazing people in the mental health advocacy community who can offer support and understanding, even without having my same illness. These people understand. But, for the general public, please be a bit more mindful when it comes to people's illnesses. Instead of screwing up your face and saying "Huh? Is that a real thing?" when they tell you of their chronic invisible illness, ask for more information out of genuine interest and concern. Something like "I'm not familiar with that, can you explain a bit more about it?" (but only if they want to, not everyone loves talking about their illness). If it's a close friend or loved one, see if they have resources. Or offer to help them find resources if they're getting frustrated at the lack thereof. Offer to go to a doctor appointment with them (if they want) in order to learn more. Sometimes a fresh set of eyes/ears can help. But please, whatever you do, don't say "But you don't look sick."