Regarding the OP, I really want to point out that mania or hypomania isn't always euphoric. It can look like and be experienced as restlessness, anxiety, irritability, distractibility... I wouldn't question the diagnosis based on not having those high states anymore, and especially not if you're medicated.
Take everything else I say with a grain of salt.
I have read that with time, people tend more towards depressive episodes, and perhaps spend more time symptomatic.
The simple truth is that the course of any mood disorder is not set.
It's generally known that "the more episodes" a person has, the more likely they are to have more, and the worse they're likely to be. And in general, the course of Bipolar I vs. Bipolar II vs. Ultra Rapid Cycling Bipolar will look different. The latter is harder to treat, and obviously there are more episodes, etc. People with Bipolar II also generally have more episodes than those with Bipolar I.
So the crucial thing is probably finding a really adequate treatment as soon as possible, which is definitely not easy. Then, if that treatment starts to falter, aggressively working to fix that.
Now, I'm saying this as someone who's basically been in an episode of depression for close to five years, with some brief moments of normal functioning, and some subthreshold hypomania or mixed states... And I've been trying different drug combinations the entire time, with ECT thrown in. Maybe the most important thing for a prognosis is the luck you have in getting diagnosed early and finding a working treatment quickly. I'm 35, been symptomatic since I was 11, and was diagnosed when I was 28, after a decade of having antidepressants and stimulants thrown at me for either depression or the ADHD that I never had.