The symptom you describe can result from sudden blockage of eustachian tube(which connects nose to ear). It maintains the equillibrium between external pressure and ear pressure.
You try swallowing saliva 2 3 times or drinking a glass of water when you experience this next time.
If this doesn't help I'd advice you to consult an ENT specialist
and get yourself examined for any growth which may be blocking the tube.
Hope I have clarified some of your concerns.
Please do get back for further queries.