I get similar things happen after a very hard workout but I get the added joy of ringing in my ears as well… I get the ringing come and go all the time but especially after hard workouts. Drives me crazy at times.
I just had the ear-popping experience for the first time (when not changing altitude anyway) at the finish after a very long event in pretty serious heat.
After crossing the finish I became extremely dizzy & nauseous. Some event personnel came to check me out, and began to dump ice water on me & put cold packs in my bibs, under my arms, and on my neck.
When they realized that this was not helping matters, a medic wheeled me back to one of the ambulances they had on standby. My ears definitely were making noises & plugging up, but I can’t remember exactly when it started. It was either just before they started the first IV bag, or just after they started it, because I mentioned it to the medic when I noticed it. By the time the second bag was drained, the ear plugging issue was resolved (10-20 minutes).
In my case I can’t say it’s a first sign! The EKG they performed in the ambulance showed an arrythmia, and the blood pressure cuff inflating caused trousseau’s sign (forearms & hands seized involuntarily when blood flow was restricted…) I had tunnel vision, and confusion… There were all sorts of dehydration related problems happening before the inner ear issues started (for me).