What exactly is PMS?

Hi. I've noticed before I get my period some of the same stuff happens. Besides physical things, I tend to get emotional. When I was going through a break up, that's when I'd contact my ex or cry about the situation. Anyway. It's really strange and freaks me out. It's happened continuously and sometimes I notice the date and feel like ahh that explains it.

Anyway, I'm wondering psychologically, biologically, hormonally, and all that, what really happens? Do dopamine levels go down?

And is how you feel before your period really how you feel, but are suppressing it the other days? Because I can be fine about my ex or seem it, then around my period, I realize I'm not that okay.

And I think it's slightly crazy that this happens.

What's the reasoning behind it?
What exactly is PMS?
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