The One You Don't See Coming

Deep in the forest of Ashanti people the elders often told the story of the mystical creature called " The One You Don't See Coming".  This animal waits until night to hunt. Silent as a leopard he creeps in and steals the brains and thoughts of everyone until morning comes.  The elders say no hunter has ever caught him.  If one caught him he would be the greatest hunter of all time.  Three young hunters decided to track and capture "The One You Don't See Coming".  They searched the edge of the forest for tracks, but found none.  They traveled deep into the bush hoping to hear or smell it, but they could not.  At a watering hole they decided to wait for it to come, for all animals must come to drink.  One climbed out on a branch of a tree next to the watering hole.  The others waited in the bush to attack it when he spotted it.  Twice, the creature climbed up the tree and tried to attack the young hunter. His eyes began close, and his head began to fall to his chest, But he recovered and yelled for help.  But before his friend arrived the animal was gone.  A third time the creature climbed up the tree and grabbed the young hunter and flung him down into the water below.  He screamed "I got him I got him", but when his friends arrived he was again alone.  "How can we hunt animal that can not be seen or heard or smelled? You almost see him but you never do." "The young hunters discovered the elders were correct. And they gave up the hunt for "The One You Don't See Coming".  Riddle: What steals your brains and thoughts just for a few hours and when morning comes you are whole again?