Herbert Spencer, the nineteenth-century philosopher, has frequently been dismissed as a "fantastical hypochondriac" (as his most recent biographer, Mark Francis, terms him). Yet he left a record in his Autobiography of symptoms that suggest a very different diagnosis. Abruptly at age 35, he found that the activity of reading, previously indulged in without difficulty, triggered paroxysmal episodes of disturbing "head-sensations" including "giddiness" (so Spencer described them); these severely curtailed his ability to carry out his philosophical studies. Of all possible explanations for such episodes, none seems as likely as reading epilepsy. Enduring preconceptions about Spencer's presumed neurosesmay have kept modern historians from appreciating that Spencer suffered from a legitimate, if esoteric, neurological malady.