Does this employee’s medical condition rise to the level of a disability?

Q: “I have developed some issues with my health and I have a note from my doctor that reads the following: ‘Ryan has been evaluated for health concerns that are exacerbated by higher altitudes such as those in Laramie, Wyoming. It would be in his best medical interests to do the majority of his work and living at altitudes similar to Denver or lower.’ What can my company do? Can they fire me?”– Ryan, Wyoming