1. To be alternately happy and sad, as due to depression or a traumatic event. My dad's been quite up and down ever since he lost his job at the factory. I was really confused as to why I was so up and down after having my baby, until my doctor told me about the baby blues.

2. To go back and forth between success and failure. Things were a bit up and down in the first few years of the business, but now we're seeing stable profit growth each month.