I'm not entirely sure where one should draw the line between neurological and mental conditions, although I suppose that a problem which could be conveniently traced to (say) a chemical imbalance which had arisen from some external cause would certainly fall on the former side of the line.

Things of that nature – chemical imbalances which aren't a problem generated by the mind but whose effects happen to impair its functioning – don't worry me particularly. I mean, I'm aware that they could happen to me just as they could happen to anyone else, but I don't lose sleep over it.

I think all the things that terrify me are the things where the mind manages to get itself into an undesirable state simply by the normal means of processing its input, thinking and adapting itself.