Post-Orgasmic Illness Syndrome (POIS), is  a rare and poorly understood illness affecting men. POIS is defined by flu-like symptoms directly after ejaculation, including runny nose, congestion, itchy eyes, sore muscles and throat, headache, exhaustion, feverishness, cognitive impairment, and difficulty speaking. (It's not the same as post-coital tristesse or dysphoria, a condition that results in intense feelings of depression after orgasm; while post-coital tristesse seems to affect men and women alike, POIS predominantly affects men.) According to a newly published review of available research, around 50 cases of POIS have since surfaced in medical literature; other known indicators of POIS include irritability, inability to focus, patchy memory, and depression.
A person who exhibits one or more of those effects at least 90% of the time is considered a likely candidate for POIS, particularly if their symptoms last for two days to one week and disappear spontaneously thereafter. Researchers don't know what causes POIS, but there are a few possible explanations. One hypothesis points to a chemical imbalances in the brain, while another suggests a semen allergy or an autoimmune disease. Currently there is no known treatment for POIS, partly due to the rarity of the disease. For this reason, those who have it are left to manage the effects on their own. POIS also often goes undiagnosed, in large part due to the stigma surrounding masturbation. What is clear, however, is that POIS can easily derail someone's life. Not only does it potentially interfere with patients’ daily schedules, but it also makes relationships hard to sustain, creating deep internal conflict surrounding sex and intimacy. These days, affected patients take antidepressants, which  keeps the acute effects of this symptoms in check; this way , they can reach orgasm without feeling like they got hit with a truck the next morning; and indeed, there is some evidence that certain classes of antidepressants—for example, selective serotonin reuptake inhibitors (SSRIs) like Prozac—might work for certain patients.
Doctors say that antihistamines, benzodiazepines (also known as benzos), and "hyposensitization therapy with autologous semen" (i.e., the patient being injected with his own semen, thus supporting the hypothesis that POIS is caused by a semen allergy) have also shown promise as potential treatments.
But if doctors don’t know what causes a disorder, they have few tools to treat it. That's why a lot of people suffering from this condition hopes putting this out there a little bit more might help someone put a name to this crazy thing.