Having a major episode of severe depression right now. Been like this the entire day, and it became even more glaring towards the night. To the extent where I don't know what to do with my hands, let alone find any activity that I find pleasure in. According to the MOE clinical guidelines on depression, these symptoms are pathognomonic of clinical depression:

Sleep increase/decrease - ok, only 4 hours of sleep last night. May be the aetiology.
Interest in formerly compelling or pleasurable activities diminished - didn't even take a second look at my fish tank.
Guilt, low self esteem - yes, I "don't know what to do" when I should / could be studying. Or jogging. Or whatever.
Energy poor - definitely
Concentration poor - Was watching LOTR part III and gazed at a 4th dimension for half the time.
Appetite increase/decrease - Mine swung from ravenous gluttony to feeling nauseous at the sight of food, all in the space of 1 hour.
Psychomotor agitation or retardation - Being retarded has always been an innate ability. Agitation, yes. Lost count of the number of nasty thoughts today.
Suicidal ideation - not yet, not yet.

Right. 4 of these criteria lasting for 2 weeks herald the onset of unipolar depression. I've got 7 of these, but only for 1 day. Probably PMS kind of depression - physiological. Shall say no more.

Perhaps it'll clear up by tomorrow.