CS Lewis died after a number of health complications, which started in 1961. He first suffered inflammation of the kidneys, followed by blood poisoning. He recovered for a short while, but then suffered a heart attack after falling ill again, which left him in a coma for nearly a day. He left hospital after waking from the coma and was forced to resign from his post at Cambridge as a result of being ill. From then on his health rapidly deteriorated and his earlier kidney problems left him with end stage chronic renal failure. A few months after leaving hospital, on the 22nd of November in 1963, Lewis collapsed in his home and died. He was 64 when he died. His death came just a few days before his 65th birthday.
His death took place on the exact same day as the assassination of President JF Kennedy, which means that the popular author’s death was somewhat overlooked as more focus was placed on the other event.