Teacher Zach Nelson spent most of his Sunday preparing for the week ahead, working deep into the evening. He put his 5-year-old son to bed, then returned to his laptop to continue with his lesson plans.

Zach felt tired, even dozing off a few times. But it was late, so each time he awoke, it made sense.

Then he awoke in the intensive care unit. Four days later. That made no sense.

On Jan. 22, 2017, Zach's wife, Leah, had gone to bed but was restless waiting for him to join her. Then she heard what sounded like a choking sound. Thinking it was the couple's dog Ike, Leah called for Zach to check...