Charles Darwin suffered for much of his life from a mysterious illness, which caused him gastrointestinal distress, heart palpitations, vertigo, dizziness, and a variety of other symptoms, and caused him to avoid leaving home for years. There's plenty of speculation about the identity of the illness:
Over the century since Darwin's death, proposals for an organic aetiology for his symptoms have ranged from Chagas' disease and arsenic poisoning to narcolepsy and diabetogenic hvperinsulinism and myalgic encephalomyelitis. Others argue for a psychiatric determinant, finding Darwin's somatic complaints to be a manifestation of a repressed hatred for his overbearing father. A third group posits a combination of organic and functional forces.
I even came across one guess that Darwin's real problem was lactose intolerance. But after reading the following passage from Darwin (which I found here ), my bet is that the illness was panic disorder:
Fear is often preceded by astonishment, and is so far akin to it, that both lead to the senses of sight and hearing being instantly aroused. In both cases the eyes and mouth are widely opened, and the eyebrows raised. The frightened man at first stands like a statue motionless and breathless, or crouches down as if instinctively to escape observation. The heart beats quickly and violently, so that it palpitates or knocks against the ribs... That the skin is much affected under the sense of great fear, we see in the marvellous manner in which perspiration immediately exudes from it... The hairs also on the skin stand erect; and the superficial muscles shiver. In connection witih the disturbed action of the heart, the breathing is hurried. The salivary glands act imperfectly; the mouth becomes dry, and is often opened and shut.