这些形容词都表示“发疯的、精神错乱的”之意。
crazy : 通俗用词，指极度的神经错乱或精神失常，也指对事物的狂势，失去自控能力。
- I seriously think she'll go crazy if she doesn't have a holiday soon.
我真的认为她要是不马上休假的话会发疯的。 - If I sat home and worried about all this stuff, I'd go crazy.
如果整天坐在家里为这些事情担心，我会疯掉的。
mad : 语气比crazy正式，但系普通用词。通常指人精神狂乱，完全不能自我控制的一种病态。
- I think I must be going mad.
我想我肯定要疯了。 - Do I look like some mad old woman in this hat?
我戴上这顶帽子看上去像个疯老太婆吗？
mental : 通常指患有精神病的。
- The family has a history of mental disorder.
这个家庭有精神失常的病史。 - A doctor was asked about the mental state of the prisoner.
一名医生被询问狱中服刑人员的神经状态。 - She had a mental picture (= a picture in her mind) of how the house would look when they finished redecorating it.
她脑海中已有了房子装修好以后的样子。
