[john samuel]

john samuel asked the Naked Scientists:
   
I was under the impression that feeling sick from spinning was the brain being tricked into thinking it was poisoned. Apparently when you are poisoned it would create similar conditions in the body, so you would vomit to rid your body of the bad berries or whatever you may have ingested. Biofeedback at its best?

What do you think?

[David Cooper]

There are balance organs in your head (near the ears) which have circular tubes filled with liquid. If you rotate, the liquid in these tubes will try to stay still and thereby move through some of the tubes, and that movement will be detected by hairs. You can see why this happens if you scatter dust on the surface of a cup of water and then rotate the cup - the water does not rotate with the cup. However, if you spin it for a long time, the water will begin to rotate with the cup and it will rotate faster the longer you keep rotating the cup. This is due to friction. The same thing happens in the balance organs in your head, which means that when you stop spinning round, the water in the tubes will keep moving for a while and tell your brain that you're still spinning even though you've actually stopped. There is no connection with poisoning. If you want to get back to normal quickly after spinning round for a long time, just spin the opposite way a few times and you'll be able to walk off with reasonably good balance.

[chiralSPO]

I read the question not as: "why does spinning make me dizzy/disoriented?" but rather: "why is being disoriented associated with nausea and vomiting?"

There are several naturally occurring toxins that also cause disorientation (ethanol, nicotine, hyoscyamine etc.) and perhaps could have presented a selection bias for creatures that vomit when disoriented. A plausible explanation, but I have no idea if there is any evidence of that theory.