the condition of being seriously mentally ill精神错乱,精神失常
He was found not guilty of murder by reason of insanity.他因为精神失常而未被判犯有杀人罪。
He suffered from periodic bouts of insanity.他患有周期性精神失常。
an action that is stupid and likely to have extremely bad results疯狂;失去理智
It would be insanity to expand the business now.现在扩大经营规模简直是疯了。