A philosophical depression, generally concerning an existential value state of mind which causes it's "victim" to go around and around and around in a never-ending loop of hellish neutralism. This depression usually lasts a while, is rare, and is a very unhealthy way of living. Unlike normal depression, nobody else can pull a person out of philosophical depression, only the philosophically depressed person can pull themselves out of it, though it is generally extremely difficult as the person would usually have to have some sort of epiphanic experience to overcome it.
Note: 'Depression' and 'Philosophical Depression' are NOT the same thing.
(Some people who have experienced it and have overcome it claim that they've simply learnt to use the depression to their advantage. Nobody can explain how, as it is supposedly verbally in-explanatory but makes sense within experience).
Typical person with philosophical depression:
*Walks past family in a window celebrating with love and happiness around a Christmas tree, walks past a woman screaming with fury at her friend*
Thinks to him/herself
"Why does everybody seem like they're acting all the time..."