Hi DragonflyK. Welcome to PC.

Bipolar typically becomes more severe over time, and frequently takes a long time to diagnose correctly. Genetic predisposition and life stressors play a part in whether, when and how it will show up.

As you experienced, it is often depressive symptoms alone that cause us to seek help.
The fact that you didn't identify any manic or hypomanic episodes over the last 10 years doesn't necessarily mean you weren't being influenced (mildly) by your biological make-up. I have asked myself the same question, and concluded that I was undoubtedly influenced for much of my life by that dizzy, frenetic, excessive, distractable, impulsive biochemical cocktail that we call hypomania.

A diagnosis is just that: a diagnosis. It doesn't mean that the illness hasn't been there all along - just not severe enough on the mania end to ring loud alarm bells.

A pragmatic question related to the above is "have I been making my illness prognosis worse by not treating it differently until now?". Unfortunately I don't know the answer to that, and the question is most relevant to the thousands of bipolar people who haven't yet received an accurate diagnosis.

I hope you find your answers soon.

TS