a play on "hypoglycemia" (low blood sugar). for some of us, low blood sugar will often cause irrational thinking which is usually hostile or depressive, or just highly irritable at best. the psychoglycemic person often cannot recognize that this is the problem, even if they are normally well able to be aware of and deal with their emotions.
Boy and girl have been dating for ten years, and have a healthy, fun relationship with easy, honest communication. They are on a long series of plane rides, and breakfast was about eight hours ago.
Boy suddenly says, "Jesus fucking christ, do you have to BREATHE like that? It's fucking obnoxious."
Girl has seen this before, thinks "Eek, he's psychoglycemic", acquires food for Boy, Boy returns to normal level mood where Girl's breathing doesn't bother him (and hasn't for the past decade).