Hi Don, and thanks for your response.  I agree with your statement about being careful of unwittingly making ourselves vulnerable.  I always say it never hurts to be too careful.  I will check out the site you mentioned about psychic self defense.  
If there is such a thing as harrassing spirits who try to take over the body, I would think any power they have feeds off our fear.  But on the other hand, as scared as I was, there must be something else about me, about my nature, that is strong enough to not be overtaken by such a low-level spirit, even if I am consciously unware of what that something is.  Or perhaps if I had been on drugs, drunk, or not playing with a full deck I might not be so lucky as to dodge a menacing spirit? 
Well, I haven't been scared off yet.  I will keep exploring, as I am too curious not to.  However, I will take the advice of using a preliminary prayer for protection.   

Vicky