If you are visiting Jackson for the eclipse you should know that we are at 6,237 feet. If you are from a lower elevation you have a chance of developing altitude sickness here, especially if planning on doing any hiking higher up. Altitude sickness is caused by the brain and lungs not getting oxygen as easily as they are used to due to the thinner atmosphere.
Altitude sickness can make you feel dizzy, cause headaches, fatigue, poor sleep, and nausea. If experiencing these symptoms while hiking, retreat to lower altitude, take ibuprofen and stay hydrated. In very severe cases people may exhibit not being able to walk straight, deep confusion, or blue lips and fingernails. If you do notice these more severe symptoms in yourself or others seek out medical help.
To prevent altitude sickness you should make sure you are properly hydrated, try taking ibuprofen 6 hours before and then during any hikes, avoid alcohol, take things slow, and eat plenty of carbs.