The World Day of the Sick is a feast day of the Roman Catholic Church which was instituted on May 13, 1992 by Pope John Paul II. Beginning on February 12, 1993, it is celebrated every year on the commemoration of Our Lady of Lourdes, for all believers seeks to be "a special time of prayer and sharing, of offering one's suffering". 
Pope John Paul II had been diagnosed with Parkinson's disease as early as 1991, an illness which was only disclosed later, and it is significant that he decided to create a World Day of the Sick only one year after his diagnosis.  The Pope had written a great deal on the topic of suffering and believed that it was very much a salvific and redeeming process through Christ, as he indicated in his apostolic letter Salvifici Doloris.
The feast of Lourdes was chosen because many pilgrims and visitors to Lourdes have reportedly be healed by intercerssions of the Blessed Virgin. The pontiff was also fond of the sanctuary of Harissa in Lebanon.
In 2005, the World Day of the Sick had a special significance since it was the year John Paul died from a sepsis. Many people had gathered around him as he lay dying.