After nearly a year of treatment and some psychological tests, I received something like a diagnosis. I remember "somewhere on the bipolar spectrum" and "mixed states".

Mixed states explain much of my life. Depression with frenzy activity, euphoria while thinking about my death, exhaustion and racing thoughts… Yes, it could be right. Especially the last year was full of it. It wasn't much bad, but it was endless. My longest stable period lasted about two weeks…

My baseline is mixed state BD1. I know how miserable mixed states can be. It sounds like the depth of mixed wasn't as hard for you as the relentlessness was. Either way, mixed states are energy draining and exhausting.

Random question: is it common that the strictly divided and crystal clear episodes change with time into such a horrible mess? Am I the only one?

Very common. For me, that how BD is.

I feel completely fine now. It's easy to think that I'm finally cured. I thought it about three months ago, but then another nice mixed episode came. Nevermind. My belief is stronger than reality.

Bipolar disorder is like that. It's a trickster. What you've explained is the main reason why so many with BD go off meds. "I'm okay now, why should I stay on meds?" Then the inevitable - a crash into an episode.

What if my so called "problems" are just my character? Everybody has mood swings, right?

I've never met anyone, online or in person, who doesn't question their BD diagnosis. Much of the nature of BD is about range of moods, rather than change of moods. A Wider range of moods a more extreme depth to moods indicates BD.

Does the diagnosis matter?

It matters to me because my dx indicates which meds will (and will not) tend to work for me. It matters because it's easier to find other people who know what it feels like to live with BD. And of course, it matters because of insurance, so I can receive proper treatment.