1.) The term "bipolar disorder" means, simply, someone who has experienced a manic or mixed episode that is not caused by drugs or organic disease. After one psychotic break the risk for a second, third, etc., is extremely high, so it makes sense to take antimanic drugs, but a significant minority of patients have only one episode or improve over time to the point that they may not need daily medication.
A lot of doctors will say "you have a serious brain disease that requires lifelong medication". I wish doctors were more open about how herterogenous the course of bipolar disorder is in real life. Most patients do need lifelong medication though, I know I probably do. If you look at the natural history of the disorder before medication, some patients had many hospitalizations when young, then were basically fine for decades, then got sick again in old age. Some got sick every year like clockwork. Some were more or less always sick. If you average together dozens of charts you can see a tendency for things to get worse without medication but there's no way to predict how any individual patient will fare.
2.) You will probably experience serious depressive and manic relapses even taking medication. 80% of patients on lithium experience a serious relapse within 5 years. Prophylaxis doesn't prevent episodes, it ideally makes them less common and easier to manage. You need to take extra meds (usually antipsychotics) during these times or you're liable to end up in the hospital or humiliating yourself etc. You need to plan for relapse. After how many nights without sleep will I take a risperidone? That kind of thing.
A lot of doctors will say "it's like diabetes and your meds are insulin". This is irresponsible and (afaik from reading stuff on pubmed) usually false, it's not something that will go away just by taking medicine for most people.
3.) "Mood stabilizers" can have cognitive side effects but you don't have to accept them. I've found myself feeling pretty free and more small-c crazy for the last year by carefully lowering lithium just a bit with a doctor but so far haven't had any worsening of real psych problems. The cognitive blunting should, ideally, be something so minor it'd only show up on a psychological exam. If it's been 6 months+ since your hospitalization and friends are using words like "low key" and "tamped down" to describe you you should seriously consider an adjustment.
I had a doctor say "you probably won't be as quick-thinking as you used to be because you have to take these drugs now"
4.) Most people who experience manic episodes have significant psychological and lifestyle problems besides their actual breaks from reality that they need to deal with, one of the biggest of which is often...
5.) Alcoholism is a serious risk in this disease and in many ways it's harder to deal with than florid mania. You can fix mania with a shot in the arm but using alcohol constantly is a lot tougher. Learning to have fun, to sleep, relax, manage stress, and be close with people when you're used to drinking heavily all the time is very hard so you need to be careful not to go down that path.
6.) You need to keep a mood journal. This should contain nothing but how many hours you sleep and the presence or absence of specific ICD-10/DSM symptoms. You should keep a separate journal for your actual thoughts and feelings. The mood journal will become really useful over time in trying to evaluate how med changes are effecting you and so you have good objective info for your doc. Instead of "Umm I think I did feel a bit up in early March" you can say "I've been having increasing subsyndronal symptoms for a few months: a week of reduced sleep but still generally over 5 hours, then normal for a few weeks, then another "up" week, and haven't actually had a hypomanic episode"
7.) You don't necessarily have anything in common with other bipolar patients. It's too easy to go online and read biographies of people like Vincent van Gogh and think "well that's me, I'm really super screwed up". You can avoid becoming that bad. There are loads of people walking around with the same diagnosis but you'd never be able to tell because they're not drunks and they take care of themselves. And ofc you'll probably have significant problems at times even when you do take care of yourself but you can make sensible choices to point things in the right direction.