The laughing attacks weren't part of his mental health condition. His mother trained him into it.

In the hospital he tells her she made him carry the card because she said it was a condition, but he realised it wasn't. She kept saying he was a happy child. He was never happy. He laughed a lot because it was a learned behaviour, what mother expected of him. It was was lasting effects of abuse. He realised he did it because she made him, so that's why he killed her. He realised she was mentally ill. He had looked after her, then realised she was his abuser.

He laughs later, but not in that same way with the choking and stuff. Later laughing is his own brand of crazy.