Drain your well tank and check the air pressure of the tank most well tanks should operate at around 38 PSI pre-charge. If there is no pressure in the tank the air in your lines is because the bladder inside the tank has failed. DO NOT DRINK THE WATER until you have confirmed that your well tank has failed or not. Replace tanks that are more than 10 years old. Look at the date stamp on the tank. If you cannot find a date stamp get rid of the tank. Has anyone been servicing your water treatment equipment latley? The air could have come from this as well.