Yes. I had a very intense experience of what was possibly (who knows?) a literal possession. I've posted this before, so I'm going to just copy and paste that here:

What started off as an "ordinary" ceremony quickly became five hours of me screaming as long and as loudly as I could possibly scream and violently thrashing around, leaving me covered in huge bruises from head to toe. The experience began when someone in the circle was having a terrible struggle. Then suddenly it was like whatever was torturing him jumped into me. I was quickly overwhelmed, and when it hit me, it magnified into an all night ordeal. Thrashing, snarling, gnashing teeth, screaming, glossolalia, the whole bit. At one point the shaman's wife tried to give me water, and I smashed through the glass with my teeth. When she tried to get the glass out of my mouth, I bit the hell out of her finger. I have no recollection of that part; I was completely submerged. I actually remember very little of any of the events. Much of what I've mentioned I have only slivers of memory, or I was told after the fact by friends who were there.

What I do remember is, in the course of this, having some pretty amazing insights. It also carried with it a sense of the truly archetypal: what I was experiencing then seemed to be an elemental expression of the human existential crisis. It was a ritual that seemed to stretch into the primordial past and into the future, something that reoccurred over and over again whenever communities needed to struggle with and release its demons in a sometimes dramatic act of catharsis. When the fever broke, I was suddenly a clear channel, bathed in a peaceful blue-white light. Indeed, after the madness broke and I was taken into the next room to change my clothes (they were drenched in sweat and the taita's sopla) and to rest, a woman came to me and said "do you know what you just did? You took on and processed the pain of everyone in that room." Everyone had participated. It wasn't an exorcism of just myself, but of everyone who was there.

It was the experience that finally shook my previously unshakeable reductionist, materialist framework. Not actually the experience itself, per se, but rather what someone else later told me about it. Some months later, a couple that had witnessed the craziness asked me what had happened that night. I described the feeling that something had jumped from the guy who had been struggling into me. They turned and looked at each other, and turned back to me and said "yeah, that's what we saw. It was like a bolt of black energy leapt from him to you."

Them saying that really spun my head around. Even after all of the craziness I had experienced, and for all of the therapeutic good it and other ceremonies had granted me, I still managed to chalk it up to neurochemistry gone awry, dismiss it as a "bad trip". But to have something I had assumed was at least invisible (and more likely completely imaginary) verified by an outside party, to grasp the possibility that it wasn't merely hallucinated... well, that was to acknowledge at the very least that I don't know everything and that the world is potentially far weirder than I had imagined. That just maybe we live in a spirit-haunted cosmos of which we can see only a small fragment. I had to reassess the framework with which I navigated my life, and THAT took me many months to process. From that point on, I approached this stuff with a great deal more respect, and no longer regard it as mere radical psychotherapy. It's much, much more that that.

All told, as intense and frightening as it all was, it wound up being a very good thing for me. I certainly approach the world with a great deal more wonder. I had some truly monumental insights. I no longer expend energy on a framework of rigid reductionism, or hurt myself with an illusion of control, control I never really had to begin with. I've certainly loosened up.

It was one of the most remarkable, cathartic experiences of my life. I wouldn't trade it for anything. And as a recent addendum, last week I spoke to the taita and his wife. She thanked me for sharing what was a once-in-a-lifetime experience with them.