depersonalization
Medical term for a dissociative symptom where one feels detached from one's own body or mental processes.
Depersonalization can involve a feeling that you are not yourself.
Compound of 離 (ri, 'detachment'), 人 (jin, 'person'), and 症 (shō, 'symptom' or 'condition'), literally 'detachment-from-person condition'. The term is a modern medical coinage.