Kennedy was close to passing away before he became president
John Kennedy had just avoided dying in battle. He suffered severe injuries when a Japanese warship sunk his patrol torpedo boat in the Solomon Islands. He guided his comrades back to safety when marooned far behind enemy lines, earning the U.S. Navy and Marine Corps Medal for bravery. He also requested his return to active leadership. (These events were subsequently portrayed in the Hollywood movie PT 109 [1963], which added to the Kennedy legend.) But the additional back problem, which had affected him since he was a teenager, never fully recovered.
He underwent surgeries in 1944, 1954, and 1955, but discomfort persisted for the majority of the rest of his life. He also had Addison disease, albeit it was kept a secret from the public. His brother Robert claimed that "at least half of the days he spent on this earth were days of extreme bodily anguish." (After he was elected president, Kennedy treated his pain with injections of amphetamines, which were at the time considered to be safe and were frequently used by celebrities for their stimulating effects. The first lady and Kennedy reportedly developed a strong dependency on these injections through weekly use.) None of this stopped Kennedy from pursuing a demanding career in politics. His family anticipated that he would run for office and succeed.
