I've had this problem, too, sometimes. It's the same experience you get when you're in a plane and the air pressure doesn't match the pressure inside your body. I generally pull my cushion away, plug my nose and VERY GENTLY blow to rebalance the pressure, then replace the cushion while inhaling. That seems to do the trick. Best, Tamara (SleepApnea.Sleep-Disorders.net community advocate)