Going on a tangent but upon reading about vestibular reflexes I recalled something I used to do as a kid:

When in bed, ready to sleep, I could condition myself to believe the bed was tipping over to the side, up to the point where I would have the reflex of grabbing the sheets to keep myself from falling, similar to jolting awake up after falling in a dream.

I wonder if something could be done to manipulate these perceptions without actually zapping the brain.