Thanks guys. I searched the internet, and found no research on the topic, but did find the unexpected:

Vestibular stimulation in mania: a case report
http://jnnp.bmj.com/content/75/1/168.extract

The article reported a reduction in manic symptoms for approximately 24 hours before a gradual increase in symptoms to the pre-treatment level of mania.

From what I understand, caloric vestibular stimulation involves injecting a cool solution into the ear. That's not quite the stimulation we get from bungee jumping or taking corners at high speed, which in my view has an exhilarating and opposite effect on mania.