Men just roll over and go to sleep after sex, right? Well, one reason why men may be reluctant to cuddle after sex is a phenomenon known as postcoital dysphoria (PCD). This isn't exclusive to men, as PCD has also been reported among women.
PCD is also called postcoital tristesse or post-nut syndrome. It is defined as a counterintuitive phenomenon characterized by inexplicable feelings of tearfulness, sadness, or irritability following otherwise satisfactory consensual sexual activity.
In a 2019 study, 41% percent of the men reported experiencing PCD in their lifetime and 20% reported experiencing PCD in the previous four weeks. Between 3% and 4% of the men reported experiencing PCD on a regular basis.
A 2020 study found that men specifically experienced feelings of unhappiness and low energy after sexual activity (especially following an ejaculation) whereas the most common experiences for women are mood swings and sadness.
Its not clearly understood, but PCD could be due to the diverging pattern of compounds released during and immediately after an ejaculation. For example, a hormone called prolactin is released from the anterior pituitary gland immediately after ejaculation. Prolactin is known to suppress sexual behaviour.
During sexual activity, as a man builds toward ejaculation, a neurotransmitter called dopamine stimulates the experience. Among other things, dopamine inhibits prolactin. Therefore, there is an inverse relationship between the two. That is, when dopamine is high, prolactin is low, and vice versa.
So, ejaculation floods the brain with dopamine, creating a transitory spike. But, what goes up must come down. His reserve stores of dopamine have essentially been used up. That is why, after an ejaculation, there are substantial increases in plasma prolactin. This increase in prolactin is partly responsible for the refractory period, that period of time after an ejaculation when he can't continue to be sexual.