Depression
Psychiatry   Wikipedia  
Understandable (such as bereavement, major stresses)
Neurotic (high anxiety personalities, negative parental upbringingHypochondriasis
Agitation (usually organic causes such as dementia)
Pseudodementia
Pain
Importuniing (whingeing, complaining)
Nihilistic
Endogenous
Secondary (i.e. cancer at the head of the pancreas, bronchogenic cancer)
Syndromal

 Mnemonic:
UNHAPPINESS