Positive Word Negation, Negative... what?

Some words are such a hassle. Thinking about words and how we use them can sometimes make your head hurt. You paint yourself into a corner and get stuck.

Take 'happy' for example.

We know the opposite of it is 'sad'.

And we're quite comfortable with saying someone is 'unhappy',

but nobody who knew better would ever say 'unsad', unless they were trying to be silly.

And then we have 'wrapped' and 'opened'-for presents, maybe. In this case, everything seems to be OK. You can have an unwrapped present, or an unopened present. Here we're in trouble again with our word meanings. An unwrapped present can be either one you haven't wrapped yet, or one which has been wrapped and then opened... yet an unopened present is only one which has not been opened.

Our first case showed opposite states which didn't agree in their ability to be negated, our second case showed words which ran off in random directions when you negated them.

I am sure there is a linguist somewhere who can pin all of this down, but the more you think about words and theor opposites, and then their negations, a lot of illogical stuff starts happening.

clean - dirty
unclean - undirty

healthy - sick
unhealthy - unsick

wholesome - sleazy
unwholesome - unsleazy

sane - crazy
insane - uncrazy (?)

It seems like some words have the meanings 'good' and 'bad' attached, and the ones which are 'good' are the only ones which can be usefully negated. Now, why would we have things like that? Maybe because people would rather just say 'sane' instead of 'uncrazy'? Or do these words try to represent the proper human state? Are our words dictating to us how we see the world?