I believe that one of the scariest aspects of living in proximity to a person with severe mental illness is that their actions and responses are not necessarily rational, or predictably irrational, or even consistent day-to-day. Any random action (or lack thereof) is capable of triggering a disproportionate response, and there can be no warning signs ahead of time. This is mentally exhausting, since the healthy person must devote a large portion of their emotional energy decoding and understanding the current mental state of the ill person, proverbially "walking on eggshells" to avoid a negative situation.