My boyfriend regularly sleeps 12-14 hours every night..

So my boyfriend 18M needs so much sleep that when he sleeps the amount of a normal person's sleep hours he needs like a 6 hour nap during the day. If hes uninterrupted he will sleep from typically 12 am to 3 pm.. just to go back to bed at 12 am again and repeat the cycle. He is not an athlete or anything so I dont understand why he needs so much sleep. Should we be worried? Its gotten worse over the years but hes always been a long sleeper. He once even fell asleep at the wheel and almost accidentally killed himself and his siblings. Its not narcolepsy tho. He doesnt just fall asleep out of nowhere typically but the second hes slightly comfortable he will. When he was in highschool hed sleep 12 hours at night and then all through his classes.