It was an excellent episode and a great performance by Cristin Milioti. The only part I had an issue with is you had to suspend disbelief a bit with the ending. But it doesn’t take away how good the episode and this show is.
Spoiler
I find it hard to believe that not a single person decided to open a window in the house, or Johnny Viti NOT closing his window. Also, a couple of people in the house were together in a room/area. I’m not sure how it works, but does CO make everyone unconscious at the same time? If not, then someone should notice if the person with them in a room passes out. A couple them obviously passed out while standing.
Common carbon monoxide poisoning symptoms include headache, dizziness, weakness, vomiting, chest pain, and confusion.
Add to this that many were also drinking.
They likely didn't all pass out at the same time (size, health, etc), but probably initially just thought they'd drank too much and by the time they figured it out were too confused to do anything about it.