Don't know if this is something similar or not, but i have similar weird experiences every so often. Kind of hard to explain but i'll try. I will be sitting in a chair at work in front of my computer. All of a sudden this weird feeling comes over me. It feels like my center of gravity has changed. Almost like how it would feel if you were to be sitting on the wall with gravity pulling on you. This feeling can last anywhere to a few seconds to several minutes.