in one's head
Prepositional phrase
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(idiomatic, of information, a plan, etc.) Within one's intellect, memory, or mind.
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(idiomatic, of a false belief, delusion, etc.) Within one's imagination; without basis in reality.
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(idiomatic, maths, of performing a calculation) Mentally.
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(idiomatic) Anxious due to overthinking an issue.
