MY 19 YEAR OLD GRANDSON HAS ALWAYS SLEPT OR NAPPED IN A VERY DEEP SLEEP. WHEN TRYING TO WAKE HIM, YOU CAN PINCH, SLAP, HIM AND IF HE DOESN T WAKEUP ON HIS OWN, WILL NOT RESPOND. TAKES NO MEDICATION TO SLEEP, OR NONE OTHER ON A REGULAR BASIS FOR ANY CONDITION. HE IS 6 2 AND 165 LBS. THANKS, COULD THIS BE A POSSIBLE MEDICAL ISSUE?