I am also under the impression it would be best to see a doctor. Moods changing like that could mean all sorts of things. It could be a physical cause like your hormones being off, it could be mental of any type (I'm not a doctor so I'm not going to try to diagnose).

I do know that "major depression" typically is long lasting and does not always include these mood swings. I personally get VERY frustrated VERY fast, the same with anger. In many ways depression has decreased my capacity to deal with things and cause me to get swayed by negative things more easily.

What you're saying though sounds like you also have some "highs" (laughter, motivation). So perhaps anything from bipolar to ... well whatever a doctor says =)

So I agree, it could be anything , you should see a general doctor who can rule out pure physical causes and move on to mental if needed.

Take care