I just observed something weird and intriguing from my own desk chair at which I am sat writing this. Just to clarify, it's one of those kinds with wheels which you can rotate.

 

Ok, I stood up knelt on the chair, closed my eyes and gave it a spin. I then span for a few revolutions until I noticed I stopped, but; after that I was absolutely convinced that I was spinning in the opposite direction. I was not really trying to make sense of what I felt so I did actually think I was spinning for the time I had my eyes shut(I think my common sense just turned off for a second while I felt the sensation). This delusion felt very "physical" to me, I actually felt like I was spinning. In fact I urge you to try it for yourself if you have the same kind of chair.

 

Finally, my question is, can anyone suggest an explanation what was happenning and what caused the sensations I experienced?

The fluids in your ear (which tell you if your moving, and if your upside down et cetera) slosh around a lot while you spin. When you stop spinning, they don't stop sloshing. That's all there is to it.

aaahhhhhh.... I see, sounds reasonable to me. So the fluids in my ear are responsible for that part of my spatial awareness, I wonder how that works.

The specific bit is called the Vestibular system, take a read.