I don't have any answers for you, but I do have sympathy. What you're described in your OP is very common with BP, especially with mania. It's more than common actually; it's a symptom of BP.
I am absolutely sure that my father had BP and one of the reasons I am sure is because of exactly what you have described.
For example, he would become obsessively interested in one subject and pursue that subject as though he was using a jackhammer. He would sink money into *whatever* the interest was, learn all about it; it would become the center of his life. For months, even.
Suddenly BANG. Done. He would entirely lose interest in the subject, become flat, depressed, and come home from work only to sit and watch TV shows, one after another...just staring at the TV. Until the next "hobby" came along...
And come to think of it, I experience similar. For example, in February spring was showing signs of beginning. One day I felt so energized and excited that I decided to entirely redecorate my bedroom in a certain theme. I got in my car and hit the road, ended up going to 5 stores in 3 hours, blew several hundred dollars, came home, dragged all the stuff in, ordered more stuff online, and spent almost all night and the next 2 days putting my new bedroom together.
I recall sitting in the middle of the pile of merchandise I had purchased and feeling like it was Christmas morning and I was ten years old.
Then, suddenly, it all seemed wrong. Crazy. Foolish. I lost interest as if I was a different person. "Fragmented" works; I understand it.
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