Altitude pressure changes and burning in abdominal

This is a pretty strange occurrence which Googling provided no answers.

I am a Nursing Student and I have to drive to my hospital for my clinicals once a week. The road I used is a fairly easy to drive and straight road which goes up and down a hill. When driving on this road on the way to the hospital, I can sense pressure changes in my ear (like that popping feeling when you're inside an airplane) and sometimes I feel a weird discomfort around my upper abdominal area. This noticed this happen only three times consecutively which raised my suspicion. Anyways, all three discomfort were different:
-In the first one I felt that I forgot to breathe--prompting me to breathe manually and to reposition myself with the seatbelt.
-The second feeling felt that I have "enlarged organs that's rubbing or pushing across my diaphragm and pericardium".
-The third one (which happened yesterday) was more localized: I felt like burning sensation which later on caused belching and minor nausea that still persists today.

Well having a stethoscope on me, I was able to quickly assess my heart and lung sounds (it was silly to do while driving) which were all WNL. My pulse was also WNL (~80bmp). I am at 32 BMI which worried me that it might be my blood pressure. I checked today which was also normal range for me (118/78). Coincidentally, during those episodes, our lessons focused on those specific systems in order (resp, cardio, abdominal) which later gave me an impression of either stress or just more "biased-to-recent-lesson assessment" as the cause. Although when I drive I keep safe distance and keep appropriate speed (not in a hurry), and I am very calm and relaxed while also listening to music. There's nothing in my life that is causing a distraction or much tension (other than focused studying), and there is no change in my diet and lifestyle. I also have a h/o non-ruptured LAP appendectomy 5 years ago.

So anyways, I'm out of ideas and only I can critically assume that it has something to do with the change in altitude because of the timing, yet I know stress is one of GERD's best cause. I can't really say that I'm stressed right now other than the fact that I am suffering from belching and slight nausea, but no regurgitation. I have taken the maximum recommended dosage of Tums which only provided temporary relief. I also think that its some sort of gas being able to diffuse easily to the peritoneal cavity at the "right" atm/baro/alt pressure. There is still a chance of this condition being unheard of and that is the reason I am here asking this question.

[selmaS]

Hi...I am not in teh medical profession, but I wonder if several  things may be going on...since u notice this with ur ears first...could u have PND that is affecting ur stomach/abdominal area?

Ans could it be that u r stressed and the closer u get it is affecting u, that the ears being bothered may be an indication as to how close to this location u r and u r getting stressed?

Could it be sub-conscience anxiety to the class?