Is there really such a thing as spirit possession which would lead to psychosis?
From my experience and studies, all I have ever seen regarding this matter is the possibility of wrecking the correct flow of energy through your body as a biproduct of misuse of mystical practices like Yoga and/or practice of occult rituals which focus only in specific chakras — like some South American magical rituals that focus only on the 1st and 2nd chakras, causing imbalance and, therefore, psychological confusion and erratic behavior on the long run.
I have no reason to doubt your testimonial, however it’s plausible to mention that, sometimes, concepts like possession or curse are a consequence of a generational exposure to fear based religious beliefs and dogma. I am no expert in any of this, but I wouldn’t rule out the possibility of it being only a psychological dissociation due to the lack of energetic coherence in your body — which could possibly be mitigated through correct mystical practices and working on the self-esteem and self-image on the day to day life (= living consciously instead of on autopilot mode).