This can happen above 8000 feet your body will acclitimised to it usually Ayer a day or two . If fat sickness at this level take it slowly and climb down to less then 8000 feet rest for 24 hrs then climb up
Take plenty of water and take deep breath to adjust your lung to take oxygen to carry to all body part . If you have tightness in chest or cough then consult a doctor and keep oxygen handy by you
Next Steps
Take it easy for a day or two when are at high altitudes
Health Tips
Climb 1000 feet after taking rest for. A day then climb up or go down then take rest for so two let body adjust high altitude