Hypergraphia is the uncontrollable urge to write. It is not a formally-recognized disorder, although it has been embraced by neurologist Alice Weaver Flaherty in her book The Midnight Disease: The Drive to Write, Writer's Block, and the Creative Brain. It is sometimes associated with temporal lobe epilepsy. It is unclear what, if any, relationship has with the trait known as Hyperlexia.
and from Medical terms:
Hypergraphia: The driving compulsion to write; the overwhelming urge to write. Hypergraphia may compel someone to keep a voluminous journal, to jot off frequent letters to the editor, to write on toilet paper if nothing else is available, and perhaps even to compile a dictionary. Hypergraphia is the opposite of writer's block.
Temporal lobe epilepsy is associated with hypergraphia. This association has been known at least as early as 1974 (Waxman SG, Geschwind N. Hypergraphia in temporal lobe epilepsy. Neurology. 1974;24:629-36). A number of prolific writer may have had temporal lobe epilepsy, including Byron, Dante, Dostoevsky, Molière, Petrarch, Poe, and Tennyson.
We may have some hypergraphia sufferers in this forum