in one's head

== English == === Pronunciation === === Prepositional phrase === in one's head Used other than figuratively or idiomatically: see in,‎ one's,‎ head. (idiomatic, of information, a plan, etc.) Within one's intellect, memory, or mind. (idiomatic, of a false belief, delusion, etc.) Within one's imagination; without basis in reality. (idiomatic, mathematics, of performing a calculation) Mentally. (idiomatic) Anxious due to overthinking an issue. ==== Usage notes ==== In the senses of "within one's mind" and "within one's imagination", sometimes preceded by all as an intensifier emphasizing that the indicated information, belief, etc. is entirely and exclusively within one's mind or imagination.