What Causes Chest Pressure While Travelling To High Altitudes?

When traveling to low altitudes, less than 3,000 , i have experienced chest pressure that starts about 10 minutes at the resting elevation. The pressure is centralized across the breast area and feels like gas. I do get burps, but then I get a shallow breathing. Seems like it s hard to breathe normally. I have had like a dizziness that starts from my body and goes to my head and doesn t last long - a few seconds. Then the back of my neck becomes stiff and tight and somewhat sore. I took a tums and the pressure did subside a little, but went away completely, as did all other symptoms, after we went back to our normal elevation of about 800 . Any idea what could be the problem?