southern term for losing one's temper, "flying off the handle", etc. Note that the R.E.M. song of this title has nothing to do with religion, despite the common misinterpretation of the phrase.
it literally means "losing my temper" or "going insane" to some degree. If you would look at the REM lyrics to the song by the same name, it makes more sense, it really has nothing to do with religion.
I was pretty much losing my religion after being forced to listen to rap music by all the freshman girls at my school.