Tsundere : Do Japanese girls actually act like this in real life?

Yeah, bipolar's what I meant, too little sleep.

And aren't the other Dere's basically mood swings too?

I haven't really watched a lot of stuff with Tsunderes in it, but it seems to me like Tsunderes are less about mood swings, so much as denial. As in, they less switch between being harsh (tsun tsun) and lovestruck (dere dere), so much as they don't want to admit they have a crush/love the Love Interest and act mean, or even violent, towards them in response.

it seems to me that Tsunderes are overcompensating. they don't want to be seen as being lovestruck for whatever reason, so they try to compensate by being cold/violent.