An irresistible impulse to jump into the sea, which may account for many seafarers reported to be "missing at sea". The situation most commonly described is that of the sailor being alone, leaning over the outer rail of the ship, feeling physically tired and perhaps reflecting upon his life ashore. The forward motion of the ship appears to enhance calenture, and is rarely experienced while the ship is stationary. It is said to be most common in hot, clear and calm conditions.
Despite, little reference to the phenomenon in the 20th century, a study reported in the British Journal of Medical Psychology in 1983 claimed that the threat was as great as ever. 50% of one ship's crew of 70 had experienced an impulse to jump off the ship. Sailors experienced a desire to jump, to soar or fly from the deck. They spoke about being "lured" and "hypnotically attracted" to the sea. 4% of sea fatalities are in the category "missing at sea".
"(A)nd perhaps, at mid-day, in the fairest weather, with one half-throttled shriek, you drop through that transparent air into the sea, no more to rise for ever" Herman Melville, Moby Dick (1851).