I ask myself is
what is the difference between myself and someone who has good mental health?
I think that one difference is that they will smile even if they do not feel like it.
So a person will feel down, but they will smile, talk to other people, and laugh anyway.
Then the mood passes, and they start to feel better.
If I feel sad, I tend to focus on it, and begin to analyse the feelings.
So, in a way, I concentrate upon it, and might get into cycle of feeling down.