Caused when the Eustachian tube becomes blocked. Earblock or sinus blockages can cause differential air pressures to exist between cavities of the skull and the exterior. If it is not possible to equalize these pressures by slowing or removing the pressure changes severe pain results. Do not fly if you suspect such a condition exists or above 8,000’ within 24 hours of scuba diving. Gum chewing and jaw movement are preventives. The Valsalva maneuver consists of opening the mouth wide with the jaw wide, as though yawning. Do this over and over because opening the mouth helps open the Eustachian tubes. Next, pinch your nose closed, shutting the mouth, and blow gently as through your nose.