for some reason I happened to find this thread and felt it was very important I replied. I am a professional psychic medium and have worked in this field for many years. I have a couple of sites, on one of them I teach a wide range of subjects all in this area.
Firstly I need you to know that possession is NOT possible. There is no way spirit can enter the body of another person, if they could I am sure that we would hear about this happening alot more.
Secondly, sadly the media has a lot to answer for with regards to giving out false information to the general public about the existence of negative spirits.
Negative Spirits do not exist and anyone who understands spirit at a deep level will be able to explain this to you.
Thirdly Spirits do not haunt houses or get stuck on the earth plane. The spirit world isnt a place as such .. as a world without matter would not have time or space (Einstein's E=MC2 is evidence of this) Spirit is omnipresent which is the ability to be everywhere at the same time.
Houses can retain residual energy which gets charged up and when sparked off can show like a film that would replay over and over (like a hologram) .. this is what we call a ghost and it cannot harm you as it has no mind (its more like a glitch in the matrix or an imprint of the past)
If you would like some more help understanding all about this feel free to drop into http:// http://www.like-mindz.com/
We have completely free classes and great chatrooms were we share experiences and even practice readings.
It sounds like your aunt has some involuntary twitching that happens when she relaxes.
Hope this helps a little.
Love Jo xx