I left a solo hunt once because of this issue. I was so mad at myself afterwards that I think it helped me deal with the problem going forward. Made me want to prove something to myself. I had a mild case of it the following year on a scouting trip and I just changed locations. After that I started to get ok with it. I seem to be ok with being out there alone now. And now I find myself looking forward to the time alone. I do carry a handgun and I have a Delorme inreach, so I can send my location home periodically and text my wife even without cell service. This and time out there seems to have worked for me. Being in shape is also a major factor. Being fit allows you to deal with the altitude better. Having altitude issues when solo really cranks up the anxiety.