Mustard
Those who are liable to times of gloom or even despair, as though a cold dark cloud overshadowed  them and hid the light and the joy of life. It may not be possible to give any explanation for such attacks. Under these conditions it is almost impossible to appear happy or cheerful.
Keyword: Depression, deep gloom for no reason. 
Human Indication: When you feel depressed for no reason. Like a dark cloud that destroys normal cheerfulness.
Animal/pet indication:  If your pet seems depressed for no reason