Dissociation, according to the Psychiatric Dictionary by Hinsie and Campbell, is "Segregation of any group of mental processes from the rest of the psychic apparatus; dissociation generally means a loss of the usual interrelationships between various groups of mental processes with resultant almost independent functioning of the one group that has been separated from the rest." Therefore, dissociation is roughly equivalent to a split, double or multiple personality. The same person appears at different times to be in possession of entirely different mental content, disposition and character. There are also other forms of dissociation recognized in psychiatry, as when a person separates ideas from their consonant effects; responses are not concordant with the consequences of actions or thoughts.
Here is a chart indicating severe multiple personality disorder (dissociation).
7 July 1945, 1422, Idaho Falls, Idaho -- Female
The subject has been diagnosed with multiple personality. I have seen them in action. Medication was prescribed. There are also regularly and frequently recurring severe anxiety attacks. The early childhood can be characterized as "horrific beyond belief". The result was very powerful repressed content; the subject did not recall the horrific events until very far along in adulthood. Naturally, this unconscious content was definitive in her adult behavior patterns; she was controlled by dark forces within her own psyche, implanted there as a small child.
The subject was, from infancy, controlled by a coven of satanic witches who went as far as human sacrifice and child rape by multiple individuals, in which the child was made a central figure. Her story is corroborated by her siblings, who underwent similar treatment, and by the chart itself.
Interpretation can begin at the Ascendant, Libra, which is a sign capable of "being whoever you want me to be," usually stated in astrological texts as a "desire to please everyone." The lord of the Ascendant, Venus, is in the first degree of Gemini, a dual (multiple) sign which can indicate ambivalence, or multiplicity and Venus is ruler of the Ascendant, which is the "persona". Also note that the two planets defining the chart pattern (Mars and Neptune -- and the fact that it is these two planets containing the personality pattern is highly significant) are both ruled by Venus, posited in the dark 8th.....and Mars and Neptune are cuspal, 8th to 12th, and are in sesquicuadrate aspect.
The chart pattern is a wide Bundle, defined by the sesquicuadrate aspect. Therefore, study the meaning of the sesquicuadrate (as an aspect, without reference to the participant planets here) and it will illuminate the chart. The Bundle pattern frequently (not always, but more often than not) indicates some severe childhood trauma which leaves its mark on the person for a very long time...this case is particularly powerful in that regard.
Note the conjunctions of Mercury-Pluto, Sun-Saturn, and Moon-Uranus (you would be very foolish to discount Moon-Uranus because of an 8 degree orb.) The three conjunctions are tied together by rulership into a complex that feeds on itself (the rulers Mercury, Sun, Moon operate as a "vicious circle"), and the terribly afflicted Mercury rules the central Venus (Venus is "central" for the reasons set forth in the preceding paragraph.)