Not sane. The word "insane" has been noted as someone who is "not sane; not of sound mind; mentally deranged"(via Dictionary.com). But, technically if you are INsane, aren't you IN sanity? You'd should
be healthy in the head. So, if you've gone crazy the word OUTsane fits better. Obviously with the word you mean that you are OUT of sanity. You are not fit in the head.