My mixed states are definitely a combination of high energy and low mood. I get angry, annoyed with everyone, and sometimes really paranoid. Pretty much how I feel now and definitely not much fun.

I have ultra-rapid cycling, and it's not the same as being in a mixed state. The quick cycling just means that my moods often change every few days (though I've had longer episodes of depression). It doesn't change the basic nature of my mood episodes (hypomanic, mixed, depressed, baseline), only their duration. Mixed states are usually my shortest. I think this is common.

I definitely get annoyed at people, especially doctors, who deny the existence of ultra-rapid and ultradian cycling. It most certainly exists, and is NOT Borderline Personality Disorder. The distinction is ridiculously simple. BPD is caused by underlying fear of abandonment and poor/unstable self-image. Fast cycling bipolar is a chemical imbalance that happens despite perfectly secure attachments and good self-image. I had a happy childhood and have better self-esteem than a lot of "mentally healthy" people I know. None of this fixes my brain chemicals.

Now, I do think it's likely we're currently classifying mood disorders caused by several different chemical processes as bipolar disorder. The root causes behind ultra-rapid cycling bipolar and slower cycling bipolar may well be different, though I think they both end with the same neurotransmitters out of balance, since the same meds seem to work for both.

Science does at least know that neurotransmitter levels have the capacity to change very quickly. If they couldn't, you'd have to wait a week for your ecstasy high to kick in, and we all know it doesn't work that way. So ultra-rapid cycling is perfectly supported by our current knowledge of neurochemistry.