I've skied my brains out for many years without a problem on some very high mountains....then...a few years ago I got permission to set up telescopes and camp for three nights on Mt. Evans, Colorado.
My house is at 618 ft. above sea level. We drove to Mt. Evans and set up in one day (14,240 ft.)! At about midnight the first night, the headaches began. The second day, it was 70 deg. and I was wearing insulated coveralls an a parka...couldn't get warm. By the second night, I was throwing up, and our food/water intake was probably 1/4th what it should have been. You don't care to eat or drink and nothing helped the headaches.
We bailed out on the third day and upon hitting 9,000 ft. ALL symptoms disappeared. It was a painful lesson but the sure fire fix is to lose altitude!
A doc friend said he could have prescribed a steroid but....why? Getting aclaimated makes the most sense, or simply don't go up mountains when you live at sea level.