Thanks, everyone, for your valuable input!

Lilysunshine, I used the term "ultradian" because my moods typically do cycle within a day; the longer duration is a very new development. I suppose I just assumed that if I did have a disorder on the bipolar spectrum it would be cyclothymia or bipolar II; the term "bipolar I" scares me because of its severity. Of course, that is no reason to rule it out. However, despite being euphoric, my highs have never caused me any serious issues; they typically are very enjoyable! Because of this, I am fairly confident that I have never experienced true mania, and hence am not bipolar I. Thanks for your opinion; your girlfriend is very lucky to have someone who is so knowledgeable about her condition.

MissMay, I have not been diagnosed with bpd, or any other psychiatric condition. I feel like I can relate to some symptoms of bpd beyond mood lability-dissociation and feelings of boredom/emptiness, primarily- but I have other reasons to think that I don't have bpd. My mood tends to have little correlation to my environment. It can be influenced by the environment to a certain extent- an unpleasant event may increase my depression if I am already depressed, but if I am hypomanic, it is unlikely to affect me. Thanks for responding; your insight into the differences between a bpd mood swing and a bipolar mood swing have further convinced me that I do not have bpd, and have been very helpful. = )