Clues

  1. The priest fell from above, landing on an altar. 
  2. The priest was suffering from leprosy. 
  3. A bishop forbade the priest contact with anyone from the parish. 
  4. No one recognized the priest due to his deformed body. 
  5. The priest fell because of passing out. 

Solution

In medieval times, one of the working priests in a cathedral got leprosy (highly contagious skin disease). To avoid spreading his sickness and ruining a good image of this cathedral, a bishop forbade him to make contact with the Catholics attending services in that church. They were told that the priest had to leave urgently and relocate to another parish. After hours of begging, the sick priest was allowed to watch church services from a hiding place located just beneath the cathedral's roof. Years passed, and leprosy was slowly devouring the priest. One day while watching the service, he passed out due to his health condition and fell over the edge of his hideout, landing in the middle of an altar, dying from this fall. His face was deformed to such extent that the gathered people didn't even recognize their old priest.