Looking to these videos, it seems that "demonic possession", etc... are manifestations of something that happens due to some traumas. Here again, if that helps you understand your trading neighbor, well, I am pleased you are getting some clues about any "strange behavior". LOL. 
<iframe width="640" height="390" src="//www.youtube.com/embed/Mu9jvM43H9Q" frameborder="0" allowfullscreen></iframe>

<iframe width="640" height="390" src="//www.youtube.com/embed/Mu9jvM43H9Q" frameborder="0" allowfullscreen></iframe>