I've had two bipolar diagnoses (don't ask!). It usually comes down to how often your mood switches occur. For me a manic period is once every year/few years, and last a few months. They've also told me that bipolar is usually very responsive to medication, whereas borderline personality (etc) doesn't respond well. I'm on Lithium, and tbh it's an absolute godsend. I still feel sh**ty about my life and all the cr@p I've had to deal with, but right now that is my only problem, without having to deal with the big manic blowouts I used to have.
Not sure if that helps, but hey-ho.
xx
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