detumescence, n.All

Detumescence (n.) was ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠mistaken by primitive physiology for lost vitality — hence the fallacy that every animal is sad after intercourse.