The English phrase “all in your head” refers to someone having thoughts that are disconnected from reality, or that an idea can exist only within that person’s head, without being manifested the physical world. This phrase is used quite a bit in the English language for anything that may be only in someone’s mind, or imagined. It’s one of many “body idioms” that relate abstract ideas to the physical parts of the body.
One common use of this phrase is the idea of hypochondria, where a person may feel ill or think that he has a medical condition. If he does not have the medical condition, his fear is said to be “all in [his] head.” This is a more physical use of the idiom, where the idea of illness is all in the head, i.e. the brain, rather than being actually physically present in the body.
Another use of the term “all in your head” is related to interpersonal relationships. People can be hard to read, and some people in particular find it hard to figure out the emotions of others. For example, someone might say “I thought that she didn’t like me, but in the end it was all in my head.” Here, it is the idea of a conflicting relationship that was only imagined in the speaker’s mind, and not the reality. Commonly, after the two individuals share more of their feelings with each other through conversation, it becomes evident whether a pre-existing idea was real or not.
Over time, the phrase “all in your head” has become a stock phrase for songs and other performance narrative. English speakers use it a lot in many different scenarios to describe fear, concerns, and thoughts on hypothetical outcomes or phenomena. Although this phrase is often highly idiomatic, it has also been linked to a more concrete idea in mass psychology.
Some individuals seem to have more distinct “voices” within their heads, or internal voices, that dictate their self-image or emotional state. Here, these voices could be said to be within the person’s head, and though they may not be related to anything in the external world, the professionals who treat certain psychological conditions agree that these internal voices can be quite powerful indeed. When therapists seek to dispel the power of these internal thoughts, they may console a patient, saying “it’s all in your head.”