Dressing up -- dressing down

Slow up -- slow down

These are two completely different categories. In the former there is pretty much no relation at all between the phrases and the latter are synonyms.

Bring up, in the sense of raising a topic. He brought up the matter of unequal access to natural resources.

Bring down, in the sense of stifling someone's good mood. He's constantly bringing me down whenever he sees me enjoying myself.