What is the reason for the inexplicable desire to cry and low mood?

It is possible that when life is not satisfactory, lonely or sad, you may want to cry and be depressed, which is a normal emotional response to negative life events.
If you want to cry, cry out, no need to hold back, try to vent your emotions, find friends to talk to or more exercise, eat sweets, change the surrounding environment, change the mood. After proper self-regulation, it can soon be relieved.