How can I explain that there is something blocking my vibrational field, hindering my mediumship, my energetic perception, etc., and I don't know how to remove this blockage? Do I need to perform an exorcism or a disobsession?
Difficult to understand exactly what you mean here. I would have say that if someone invites any entity into their "personal vibratory field" without due consideration as to Who/What it might be, is to simply "Pay Your Nickel and Take Your Chance"! You may get a lot more than your "medium-ship" blocked! Your question is a bit nebulous especially regarding your "medium-ship".