I wonder if this can explain the trick I learned on reddit on how to relieve the ringing-tone (tinnitus) by snapping your fingers on to your skull: https://np.reddit.com/r/WTF/comments/3l3uri/these_guys_light...

In other words, can percussion on the back of your head somehow reset/affect the nerves deep inside your head that send signals from your ear to your brain? For tinnitus, it's the audio signal. For motion-sickness, it's the balance signal.