I, too, have experienced this from time to time during and/or after class (though mostly during the first month of doing Bikram, and I am now going into month #3). I feel it to be the result of one of the following:(1) internal fluid either moving from my sinuses/eustachian tubes–kind of like you might feel when you change altitude and your ears won;t quite ‘pop’, (2) an adjusting of the top cervical vertebrae that has an effect on sensations in my inner ear, (3) the result of trying to drink water too frequently during class and it moving in the wrong direction in my head…or some combination of all 3. I can say that when I stopped drinking water during class (except once or twice, at the opportunities indicated by the teacher) the inner ear issue stopped occurring.