Negative energy, most likely. Particularly violent deaths or unhappy spirits can just swath themselves in a kind of bleakness, and it affects the air around them. The entire colony was thick with it. Even you should've felt it. That thick, cloying sense of dread in the air.

[Rei takes her tea with no condiments, setting the tray down and sipping the bitter liquid with an approving nod.]

That can affect dreams, I think.