For example, it has been proposed that overstimulation of the Vagus nerve - which suppresses heart rate in a mechanism related to the behavior of apparent death or "playing possum" - is the cause of documented cases of psychogenic death. The flight or fight response to fear or stress has the opposite effect, increasing heart rate through stress hormones, and can cause cardiovascular problems (especially in those with pre-existing conditions). This is the proposed mechanism for the observed increase in the death rate due to cardiac arrest after widely experienced acutely stressful events such as terrorism, military attacks, and natural disasters (even among those who are not in the affected area) and for documented deaths in muggings and other frightening events which caused no traumatic physical harm.[4][5] The proximal medical cause of death in these cases is likely to be recorded as cardiac failure or vagal inhibition (which also has other potential causes such as blows to certain parts of the body and nerve injuries).[6]