Don't worry too much about it. Since it has escaped for 4 weeks now, it's just not used to being put back into it's cage.
But if you are really worried about it, then take it to a vet to examin it. There might be other parasites and or other things that it has caught during the month of escape.
If you have other snakes, remember to put that one in another room so if it does actually have other disease or parasites, it doesn't get into your other snakes...
Good Luck and Happy Herping!