He had a sheepish grin on his face, almost as if he was embarrassed to be bothering us at work, which made my coworker laugh awkwardly and ask, "Wait... What? Are you serious?"
The son-in-law repeats that, "Yeah, he's not breathing".
My coworker and I had a moment of 'oh-gosh-he's-not-joking-around-is-he?'
She quickly called 911 as my other coworker ran to grab our boss, who's an RN and ex-EMT/Paramedic. Both the boss and another CPR Instructor rushed off next door, with me mostly staying in our office suite to herd two classes full of students and to keep them from crowding around too close to the doors. One of the classes going on was an Advanced Cardiac Life Support Course, the other a Basic Life Support Course (CPR, AED), and one of the students from the BLS Course turned out to be a Korean ER physician, so he dashed over next door to assist with the situation as well. Turned out to be a good thing, since the landlord's girlfriend was a witness of the cardiac arrest, and spoke only Korean, so our student was able to play translator.
Long story short, the fire fighters showed up first with the AED; it was unshockable rhythms all the way. When the paramedics showed up, we decided to let them do their jobs and have us go back to resuming our jobs/classes next door.
We joked (dark humor) to the ER physician that the events that just transpired was his exam-- which he clearly passed-- and that he would be issued his CPR certification card and could go home for the day, heh. Later on in the day, he said he called his friends to tell them what had happened, and none of them could believe it-- imagine going in to take a routine BLS/CPR Certification Course, having the guy next door go under cardiac arrest and having to go help do CPR for real on someone.