0Well, yes, you might ask that if the person does show those signs, but it's also used as MH suggests. It's the equivalent of "Are you nuts?" "Are you crazy?" etc0-
0There was an old idea that spending too long in the sun would send you insane.02br 02br 00Therefore, it is a cheeky way of saying to someone 'what you are saying/doing is nuts/mad/crazy'.0-