Don't talk to the child while they are in the time out. If they know the rules, and that you're serious, it works. My daughter who is five is very high spirited at most times, but she can also have very emotional low points. There is depression in our family history. Being tenacious gets one ahead in the world.
Some kids just are sensitive.
I would not see having low points as meaning someone was depressed. If a child were discouraged and sad and crying a lot, I would suggest talking to your pediatrician. They have a very good sense of what is developmentally within the range for a five year old. I don't remember lots of kids with depression when I was young in the 1950s. Fifteen years ago, they were arguing whether a child or adolescent could even be depressed.