Please take a look at the videos I posted links to. They show what freaking out is.
There may be differences between users. Raymott seems to disagree that freaking out can be a result of joy. He says he would call it something else. However, I have come across such usage (my own usage doesn't matter) -- the video of the excited girl is not a result of just typing "freak out" into the search box, but of a considered search.