The same intensifier as 어서 미치다, but with 서 dropped, which makes it tighter and more exclamatory: 답답해 미치겠어요 (I'm going mad with frustration), 나 이거 너무 좋아 미치겠어 (I love this so much I could die). It hooks straight onto the feeling — hot, bored, desperate to explain — and shows up mostly as 미치겠다 or 미쳐버리다. On its own 미쳤어 is slang for 'insane' in the admiring sense, as in 엄청 진해 미쳤어.