Is depression something that can come and go?
"When Words Are Not Enough" by Valerie Davis Raskin
Each of us has a one in five chance that this disease will hit us at some point in our lives, and once you've suffered an episode of clinical depression, you have a 50-50 chance of getting it again
Some illnesses can cause depression, or something that looks very like it. An under active thyroid is one such illness. You may have an odd reaction to a particular medication that causes depression while you are taking it. It may come back after a period of intense emotional stress.
It is not guaranteed that depression will return, it is not guaranteed that it will not.