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This is just my personal experience.
I knew I had bipolar because my experience went beyond regular depression. I have type II, so I go through depression and also hypomania. The hypomania and/or regular mania is what separates bipolar from depression. My APRN who prescribes me my medication went through a questionnaire with me and said I do fit the symptoms of bipolar.
When you're manic/hypomanic it's almost like you're experiencing a high, giddiness, irritability sometimes... For me I don't know what to do with myself when I am hypomanic and have a hard time sitting still. Some people may find themselves acting more impulsive or engaging in risky behavior. For me, one of the ways my impulsivity comes out is through impulsive spending... My bank account is currently suffering as proof of this I consider myself to have a lot of "anxious energy" when I am hypomanic. My thoughts race just like when my anxiety disorder acts up, and I feel like I'm going fast. I can get a lot of things done, but it doesn't feel super good to? Then with the depressive episodes, I experience your typical depressive symptoms. Sometimes there are also "mixed episodes" where I get the best of both at the same time
Bipolar is typically thought to be a long term diagnosis, but it can be managed with therapy and/or medications. One type of medication that's typically given is a mood stabilizer. For therapy, CBT or DBT can be useful (I've never done DBT myself though!). A big part about treatment is trying to notice things that may trigger an episode and trying to notice when you feel one coming on. Developing coping skills before you need them is also super important.
This link by the NIH describes more about what bipolar is.