I conceive the complex to be a collection of imaginings, which, in consequence of this autonomy, is relatively independent of the central control of the consciousness, and at any moment liable to bend or cross the intentions of the individual. In so far as the meaning of the ego is psychologically nothing but a complex of imaginings held together and fixed by the coenesthetic impressions, also since its intentions or innervations are eo iPso stronger than those of the secondary complex (for they are disturbed by them), the complex of the ego may well be set parallel with and compared to the secondary autonomous complex. This com-parison shows the existence of a certain psychological similarity, because the emotional tone of the secondary complexes is also based upon coenesthetic impressions, and, further, both the ego and secondary complex may be temporarily split up or repressed, a phenomenon which may be observed with particular clearness in hysterical delirium and other "cleavages" of personality. Especially in those states where the complex temporarily replaces the ego, we see that a strong complex possesses all the characteristics of a separate personality.
— C. G. Jung
Jung is writing in 1904, years before the vocabulary of individuation or the Self has settled into place, and what he offers here is stranger and more unsettling than his later formulations. The ego is not a given. It is itself a complex — a collection of imaginings cohered by the body's felt sense of itself, coenesthetic impressions, the low hum of somatic registration that keeps the "I" continuous across moments. What makes the ego feel like a center rather than one node among many is only that it tends to be louder, its intentions more coordinated, its grip on the body more habitual. That is all.
The consequence follows without melodrama: when a secondary complex is sufficiently charged, it does not merely interrupt — it temporarily becomes the I. Not metaphorically. The person does not "feel taken over"; they are, for that interval, another personality, another center, with its own intentions, its own coherence, its own relationship to the body. Jung observed this in hysterical delirium, but the structure holds wherever affect is strong enough to displace the usual coordinator. What you experience as your self-possession, your continuous interiority, is a matter of degree — of which complex currently holds the coenesthetic anchor. The ground was never as solid as the standing on it felt.
C. G. Jung·Experimental Researches·1904