I was on thyroid supressing medication when I moved from England to the highveld of South Africa. It was a significant altitude change. Within about ten hours of being in SA, I had palpitations, dizziness and was worried I was having a heart attack. I was also on Inderal.
I had just moved there and had no doctor. I suffered through this and after about 5 days, the symptoms dissipated. I may have been suffering altitude sickenss and that affected me psyciologically.
I do not know if anything can be done about it. If you are traveling again, it would be good to research this because I have also experienced it and you may well again.