Logorrhoea is defined as follows,

pathologically excessive and often incoherent talkativeness or wordiness that is characteristic especially of the manic phase of bipolar disorder.

Symptoms include,

pressured speech, grandiosity, increase in goal-directed activity, and decreased need for sleep.

Sound familiar?

Along the same vein, schizophrenia is described as follows,

Schizophrenia is a psychiatric disorder that affects the brain and often influences how someone talks, causing pressured speech and disorganized (difficult-to-follow) speech. Personality disorders: People with personality disorders, particularly narcissistic personality disorder, may talk excessively.

Again, sound familiar?

I guess that would help explain a certain someone rambling in coherently about sharks and batteries and boats. Have a nice day.