The phrase "is on up up" typically implies a sense of positivity, advancement or success. Its antonyms will, therefore, be words with negative or contrasting meanings. These could include: down, decline, worsen, diminish, deteriorate or stagnate. When things are not on the up up, they may be heading in a negative direction, falling or failing. It's important to note, however, that the opposite of the phrase doesn't necessarily mean total failure or doom. People may still find success despite facing setbacks or declines, and there are always opportunities for growth and improvement.