Sexual intercourse can sometimes lead to a feeling of melancholy called PCT, or post-coital tristesse (from Latin post-coital, and French tristesse, literally — “sadness”). This is more common in men than in women. With respect to symptoms in women, see "An epidemiological survey of post-coital psychological symptoms in a UK population sample of female twins."[1] Many PCT sufferers may also exhibit strong feelings of anxiety, anywhere from five minutes, to two hours after coitus. For more, see "Sex and depression: In the brain, if not the mind."[2] Possible physiological causes of post-coital tristesse are discussed in "The Passion Cycle." [3]
The phenomenon is referred to by the philosopher Baruch Spinoza in his Tractatus de Intellectus Emendatione when he said "For as far as sensual pleasure is concerned, the mind is so caught up in it, as if at peace in a [true] good, that it is quite prevented from thinking of anything else. But after the enjoyment of sensual pleasure is past, the greatest sadness follows. If this does not completely engross, still it thoroughly confuses and dulls the mind."
A better-known reference is the (grammatically incorrect) Latin phrase Post coitum omne animal triste est —"After sexual intercourse any animal is sad". The correct phrase is " Post coitum anima tristis est" which translates to "After sex the spirit is sad."
English comedian Russell Brand describes the phenomenon in his stand-up: "After I cum, it's like 'Oh my God, what have I done?' A sense of profound existential angst, a sense of loss, a sense that somehow I've let my mum down."[4]