I can relate to this a lot! Actually, even when I'm stable I have often had a tendency to hyperfocus on one or two things. I don't have ADHD, though. I don't sufficiently fit that criteria when stable. It's more of a personality characteristic for me. My hyperfocusing is more fueled by an excited semi-obsessive interest in the thing/interest at hand. But when I'm hypomanic or even sometimes full blown manic it intensifies, sometimes A LOT. I become able to achieve feats I normally couldn't. My creative and analytical abilities sky rocket. It can get so intense that everything speeds up to near wildness and can even become dysfunctional.

Another example is obsession with a person when hypo/manic. My brain goes haywire and flirtation and maladaptive daydreaming go extreme. I'll have story lines racing through my head about the person (or some situations) some changing based on reality, others all made up in my head. They can include elation and rage in the same minute.

There is an interesting blog article on this topic at https://blogs.psychcentral.com/bipol...hd-hyperfocus/ for anyone interested.