OK, this sounds a little crazy, but since you're asking: I used to smoke weed a lot in my early twenties. One time I was at home smoking bong with a friend and something just didn't feel right ... hard to explain... I just had a really bad feeling, when all of sudden my friend started to choke for no apparent reason. I saw a dark cloud occupying the same space as him. I know how crazy this sounds. Let me explain. I didn't see it with my eyes. When you visualize something, you see it in your mind. That's the way I saw this cloud thing. Now, this could have been imagination, but the interesting thing is, that I thought I saw the cloud coming. At this moment it was nothing more to me but imagination or random visual effects in my mind because of being stoned, but when he started choking at the exact moment this imaginary cloud thing moved into his body, I thought "ok, IF this is some kind of supernatural thing and the bad feeling is somehow connected to what's happening, it might be possible to send it away by using/changing my thoughts". So I sat up straight and tried to visualize spreading light and thinking "Fuck off and leave my friend alone! Now!". I looked at him and saw this cloud withdrawing from him upwards and disappear through a corner. At the exact moment it left his body, he stopped choking and took a deep breath. We both were like "wtf just happened?".