If you’re “beside yourself,” whether it’s with sorrow, joy, or rage, you’re “outside yourself” or “out of your mind.”
The phrase “beside oneself” appeared at about the same time (1400s) as “out of one’s mind,” which the Oxford English Dictionary defines as “having lost control of one’s mental faculties; insane, deranged, delirious.”
There are many other synonyms for being beside yourself: distraught, frantic, desperate, distracted, at one’s wits’ end, frenzied, joy, sorrow, anxiety, frustration, confusion, fear, worry, rage, grief, or depression, ecstasy, astonishment, enchantment, awe. Phrases which have a similar meaning are: “in the pit of despair,” “in seventh heaven,” “cloud nine.”
This expression is typically traced back to ancient Greece, where “beside” meant “outside of” or “away from.” The ancients believed that soul and body could part and that under great emotional stress the soul would actually leave the body. When this happened a person was “beside himself,” actually split in two. The Dictionary of Word Origins by Jordan Almond, 1998, says that the Greek word for ecstasy meant “standing out of the body.”
In 1490, William Caxton, the first to print books in English rather than French or Latin, translated the Aeneid from French. In the work, Caxton translates the French phrase, “hors de soi” (meaning “outside herself”) to “mad and beside herself” (with regard to Dido’s mental state when she learned of Aeneas’ departure), marking the first time the expression is used in print.
The word “mad” dates back to the Middle English of the late 1200s and originally was used to describe an aggressive or rabid animal. Soon, it was applied to people who were out-of-control and dangerously imprudent, and within a few years “mad” took on the meaning of being wildly excited as well as insane and mentally unbalanced.
An article on psychology says that the mental state of being beside oneself resembles the psychotic splitting of schizophrenia. The emotion one feels is so highly charged, or excessive, that rational faculties are no longer functioning (thus “out of one’s mind”). It’s only to be expected in such an extreme state of feeling that mental clarity would have evaporated.
The article goes on to suggest that the being who “appears” when you’re beside yourself is your inner child, the part most susceptible to being “flooded” with emotion. A child is not yet capable of summoning the cognitive resources necessary to cope thoughtfully with unanticipated situations and events. So, when you’re enraged, you may be regressing into a full-fledged temper tantrum, similar to a hyper-emotional two-year-old. Your emotional child self can’t help but think in absolutes. You can only counter this by convincing your now outer child that what just happened isn’t really as catastrophic as it “feels.”
Oxford notes that the expression is now used in the slang sense of “stoned” (also bombed, pissed, etc.), as well as “stupefied, extremely intoxicated, or incapacitated by drink or drugs,” and “bored out of one’s mind.” Also, “out of it,” an expression that meant “not involved” when it showed up in the early 1800s, evolved into a 20th-century slang term meaning “confused, stupefied, or unconscious, especially after consuming drink or drugs.”
I don’t ever want to be beside myself. One of me is plenty.