Keep him warm, and try to keep him from dehydrating, dehydration can kill quickly. Sunken eyes are one symptom of dehydration, and may be the cause of your beardy's unhealthy looking eyes. Maybe try misting him a little (during the day when the sun's up so he doesn't become too cold) to see if he'll drink some of the little droplets.
Dehydration is something I didn't think of. If he doesn't have a temperature gradient in his tank (ie warm end and cool end), he might not be able to move somewhere cooler if he wants to. Give him a tepid bath - not too warm, not too cold - a couple of times a day and see if he perks up. If it is dehydration, it sounds like it could be severe, so adding electrolytes to the water wouldn't hurt. Apparently, simple Powerade will do it - see post #14 of http://www.aussiepythons.com/forum/herp-help-38/alternative-reptile-care-167791/ for instructions on how to make an electrolyte bath.
It's something you can try in the meantime.