What is the origin of the idiom "be beside oneself" and when to use it?

The origin of the idiom "be beside oneself" can be traced back to ancient Greek mythology. In Greek mythology, it was believed that when individuals experienced extreme emotional states or divine possession, their souls or spirits would temporarily leave their bodies. This state was referred to as "ekstasis," meaning being outside oneself or beside oneself. It is often used to convey a state of being deeply affected or overwhelmed by emotions, leading to a temporary loss of control or composure.