What is a mental illness that is very dangerous if ignored?

Depression.

It is easy to ignore depression because depressed people often pretend there is nothing wrong. When the disease is severe, patients often hang out at home so nobody even notices that they are having symptoms.

Depression is often very, very advanced when it is “obvious to everyone.” It is not unusual to see depressed persons laughing, joking, and smiling at work and then going home and just shutting down.

This puts depressed persons at risk for suicide. How often do we hear, “She seemed so happy” or “he was always such a joker?” But nobody knew.

It is very dangerous to ignore depression. And most likely you know a “happy” person right now who is faking it.