Now that we've cleared up what a true Wendigo is, you might be wondering in terror what exactly "Wendigo Psychosis" entails, and if you're not, you should probably start right about now.
It's when a person becomes convinced that they are a Wendigo... most prominently marked by an intense craving for human flesh. Yes, this is a real thing, that happened to real people.
Many tribal societies were familiar with cannibalism, having to eat human flesh during dire periods of starvation and all, but sometimes the guilt and fear associated with the act was so great that it drove them insane. When you end up snacking on a dude, it's not hard to imagine yourself as a kind of monster. After all, isn't it better to see yourself as a mythical beast than just a hungry guy with low standards?
That's the best guess as to where Wendigo Psychosis comes in. But understand that once it kicks in, the victim believes they're an invincible man-eating monster regardless of how much actual food is around. When people would start to feel the symptoms coming on, they would sometimes actually ask to be executed before they could go on a man-eating frenzy. Holy shit!