There might be another reason why men roll over and go to sleep after sex: They’re not feeling so good.
Post-orgasmic illness syndrome (POIS) is a rare illness that gives men flu-like symptoms — like extreme fatigue, high fever, weakness, congestion — within about 30 minutes after ejaculation. The first case wasn’t documented until 2002, but researchers from the Tulane University School of Medicine in New Orleans say that POIS needs more research to uncover the “prevalence, pathophysiology and treatment of this debilitating condition.”
The reason why doctors don’t know much about it is simple: It’s so rare — only about 50 cases have emerged around the world — so the need for research isn’t really there. However, a couple of studies into POIS point to a couple of possible causes: either it’s an autoimmune reaction to a semen allergy, or that affected men have another underlying condition that affects their opioid receptors, including endorphins.
Sex allergies can affect both men and women
POIS might only affect men, but women can also be allergic to sex — or, more specially, semen.
"It's really a very rare condition, but it does happen," allergist and immunologist David Resnick at New York Presbyterian Hospital told LiveScience. The way women respond to the allergies differ from woman to woman: Some are allergic to all semen, while others only react to certain partners. An even smaller group of women isn’t allergic to the actual semen, but to allergens from foods and chemicals in the semen.
This type of allergy doesn’t have a real cure. Some women outgrow it, while others are treated with small amounts of semen to help desensitize their bodies to it.
The same goes for POIS: There’s no cure, but it’s typically treated with antihistamines, benzodiazepines and serotonin reuptake inhibitors. Somehow we don’t think the results of sex will keep any man from participating in it, though.