Iis that my mood is so arbitrary and out of sync?

I've been thinking about it lately and I feel as though my mood is out of sync with the events that happen in my life.
I switch from happiness to sadness or vice versa, without any discernable reason. There may be some minor details that I tend to pin down as causes in the spur of the moment but essentially... Nothing happened, my mood is just swinging like a pendulum. Like it's complety independent.
I know that mood variation is to be expected, if only because of hormones, but it just seems completely arbitrary.
For instance, I was dumped two days ago and I was okay. The day after, I was sobbing and feeling miserable and terrified by solitude.
If it was only this one time, you could say that I had a delayed reaction, but stuff like that happens all the effing time. Whether something truly important happens or not, it's similar. And the most startling is that when something important does happen, my mood doesn't always seem to correspond.

By the way, my dad is bipolar. I often wonder if I could have inherited his disorder but I'm reluctant to assume so since my mood swings aren't really that extreme, as far as I'm concerned. And I haven't had any psychotic episode (yet?).
But then again, I may have a tragically stereotypical view of what bipolarity is, I don't know.