Possession by Evil Spirit

I am eternally grateful having attended the Synchrodestiny course; as the true context of your teachings came crashing down on me when I read the first chapter of the Upanishad from your bookstore. “Blessed are they who, through an illumined teacher, attain to self-realization” (Katha Upanishad).I cried like an infant, overwhelmed by Love, Knowingness & Bliss; an emotion I had felt only as a young toddler. In my childhood I tried to keep close to the source, speaking in my own way to Jesus and to my ancestors. I remember feeling Love & Bliss and I now feel enlightened with a deep sense of knowingness that we are One, united in the Universe.

However, in my quest to get some answers during my adolescence I have
ventured beyond faith into reality. If we are all “spirits with a human experience” and our spirits are inherently peaceful & good, then how do I explain the following?

I have been brought up in a Roman Catholic environment. During my adolescence I developed an urge to see proof of this higher “might”/ God as you like it. But at that time I saw no signs. Therefore I had set out to seek proof of God by seeing proof of his opposite extreme.
One vacation, when visiting my parents in Cameroon (West Africa) I enlisted to participate an exorcism performed by the Archbishop of Yaoundé (the capital). This was all the proof I needed and it can still haunt me when I think of it !!
What or where was this “good” spirit? What made a human convulse so extremely that one would question the whereabouts of his soul? Is this human experience you talk of really inseparable from the soul? And can a soul also prove to be demonic? How do I rationalize what I have seen and heard? What does this imply to the dark side of men?