M.R.
Did you ever ride amusement/carnival rides as a kid? Weren't the ones that made you really dizzy almost to the point of throwing up the most fun ones?!?
Chances are your little boy has discovered a new way to move his body through space which includes a different, odd, yet fascinating feeling that he wants to recreate. Now, if it were me the idea of spinning in a circle makes me nauseous, but for kids it just feels really cool. Dizziness is caused by the spinning of the fluid in the semi-circular canals in the ears; the brain is just fine.
Ask your pediatrician to get clarity. The only thing I'd worry about with the exersaucer is keeping him in for a maximum of 30 minutes a day, as reliance on the apparatus to hold him up could delay core muscle development needed for learning to walk.