"Of late, anything which flurries me completely knocks me up afterwards and brings on a bad palpitations of the heart" Charles Darwin, letter to Prof. Henslow, 14 October 1837
Darwin was explaining to Henslow that he does not want to be elected Secretary of the Geological Society and came up with several excuses. This quote relates to his health and you'd think this was written by an old man worried about his heart but Darwin is only 28 at the time. I'm no epidemiologist so I won't even speculate but those that have, suggest it was Chagas disease. A disease caused by a parasite so it wasn't just specimens that Darwin sailed back with.