I was wondering if you workout at a gym or not. The reason I ask this is that I get the same feeling, but I'm allergic to the spray that you use to clean off the machines when you are done. It also clogs up my nose.
You may want to visit a doctor and talk to him/her about whether or not you have fluid in your ears. I do, due to allergies, and just jumping up and down and running and stuff can aggrevate the fluid and make it feel worse. I have an allergy to dust and I was prescribed a nose spray that helped.