Insomnia - Stephen King

Ralph Roberts used to be an ordinary guy—until insomnia robbed him of sleep. Now he's no longer ordinary—he can see horrible things happening to the people of Derry, Maine. He can see how, one by one, they are turning into monsters straight from hell.

He'd like to call them nightmares, but he's wide awake. He can't call himself crazy, because there is another person who sees these happenings, too. But even if seeing is believing, it still doesn't give him a clue of how to stop these deadly, demonic visions from coming true.