A regional way of saying and spelling 겠, the piece that guesses or predicts how something will be or feels. Four of the eight lines here are the stock complaints built on it: I am dying, this is driving me crazy, it is killing me. Swapping 겠 for 겄 adds a rustic, worn-out flavour that the standard spelling does not carry, so subtitles use it to show a speaker's accent or exasperation.