In the paired ventral part of the fin line, normally only the pectoral and pelvic fins survive (but the Devonian acanthodian fish Mesacanthus developed a third pair of paired fins); but along the non-paired parts of the fin line, other fins develop. In tetrapods, only the four paired fins normally persisted, and became the four legs. Notomelia and cephalomelia are atavistic reappearances of dorsal fins. Some other cases of polymelia are extra development along the paired part of the fin lines, or along the ventral posterior non-paired part of the fin line. Notable cases
Humans
1995: Somali baby girl born with three right arms. In the summer of 2005, a baby girl named Destiny was born with a fully formed extra leg in Detroit. This was the result of a conjoined twin scenario. In March 2006, a baby boy identified only as Jie-jie was born in Shanghai with a fully formed third arm: he had two full-sized left arms, one ventral to the other. This is the only documented case of a child born with a fully formed supernumerary arm. It is an example of an extra limb on a normal body axis.
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.