Zou huo ru mo 走火入魔

"Fire runs wild, the demon enters". The classical term for internal practice going wrong: rising heat that will not descend, agitation, insomnia, and in severe descriptions lasting psychological disturbance. The second half of the phrase is not a metaphor in the literature it comes from — see mo — and modern usage, which takes the whole term to mean something like a breakdown, has quietly dropped half of what it says.