MEMORY WIPED OUT

 One of my students, Afifi, met with an accident recently.  As a result of the accident, he has to use crutches to walk about.  When I asked him how the accident took place, Afifi said that he could not remember a thing. Everything was blank to him.  He said that the memory had been completely wiped out from his memory.  Strange, isn't it?
Just last week, I heard from Sue Lyn that a friend of hers who had gone on holiday abroad had also no recollection of his trip to the Phillipines.  It seems that the friend was surfing the Net in the hotel room and just blacked out.  Members of his family had to fly over there to accompany him back to Malaysia.  Even after being checked by the doctors here and given a clean bill of health, he still cannot remember what happened to him.
What actually happened to the two of them?  Is this a medical condition?  Or is it something paranormal?