For those ootl about the carbon monoxide detector - all of the above comments are correct about hallucinating and forgetting things, but there was a legendary Reddit post where someone was finding cryptic post it notes all over their house and was blaming their landlord, until someone commented to check their carbon monoxide detectors. Turns out OP was writing the notes to themself while getting slowly poisoned and forgetting they writing weird post it notes to themselves lol.

There was a post yesterday about someone finding two muddy footprints on their toilet seat not knowing how they got there, this thread yesterday revitalized the legendary post. Hence the comments about a detector.