They may show up as restlessness, irritability, increased sexual frustration, apathy, sluggishness, neediness, dissatisfaction with a mate, or weepiness over the days or weeks after intense sexual stimulation. Such phenomena may be part of human mating physiology itself. Sexual headache is a distinct condition characterized by headaches that usually begin before or during orgasm. Mechanism
The cause of POIS is unknown. Some doctors hypothesize that POIS is caused by an auto-immune reaction. Other doctors suspect a hormone imbalance as the cause. Different causes have also been proposed. None of the proposed causes fully explain the disease. Allergy hypothesis
According to one hypothesis, "POIS is caused by Type-I and Type-IV allergy to the males own semen". This was conditioned by another study stating "IgE-mediated semen allergy in men may not be the potential mechanism of POIS".Alternatively, POIS could be caused by an auto-immune reaction not to semen, but to a different substance released during ejaculation, such as cytokines. Hormone hypothesis
According to another hypothesis, POIS is caused by a hormone imbalance, such as low progesterone, low cortisol, low testosterone, elevated prolactin, hypothyroidism, or low DHEA.POIS could be caused by a defect in neurosteroid precursor synthesis. If so, the same treatment may not be effective for all individuals. Different individuals could have different missing precursors leading to a deficiency of the same neurosteroid, causing similar symptoms. Withdrawal hypothesis
The majority of POIS symptoms like fatigue, muscle pains, sweating, mood disturbances, irritability, and poor concentration are also caused by withdrawal from different drug classes and natural reinforcers.
Postorgasmic illness syndrome (POIS) is a syndrome in which people have chronic physical and cognitive symptoms following ejaculation. The symptoms usually onset within seconds, minutes, or hours, and last for up to a week. The cause and prevalence are unknown; it is considered a rare disease. Signs and symptoms
The distinguishing characteristics of POIS are:

the rapid onset of symptoms after ejaculation;
the presence of an overwhelming systemic reaction.POIS symptoms, which are called a "POIS attack", can include some combination of the following: cognitive dysfunction, aphasia, severe muscle pain throughout the body, severe fatigue, weakness, and flu-like or allergy-like symptoms, such as sneezing, itchy eyes, and nasal irritation. Additional symptoms include headache, dizziness, lightheadedness, extreme hunger, sensory and motor problems, intense discomfort, irritability, anxiety, gastrointestinal disturbances, craving for relief, susceptibility to nervous system stresses (e.g. common cold), depressed mood, and difficulty communicating, remembering words, reading and retaining information, concentrating, and socializing. Affected individuals may also experience intense warmth or cold. An online anonymous self-report study found that 80% of respondents always experienced the symptom cluster involving fatigue, insomnia, irritation, and concentration difficulties.The symptoms usually begin within 30 minutes of ejaculation, and can last for several days, sometimes up to a week. In some cases, symptoms may be delayed by 2 to 3 days or may last up to 2 weeks.In some men, the onset of POIS is in puberty, while in others, the onset is later in life.