There are so many reasons for a hammy to lose hair and the methods to treat hair loss usually require a vet's help. I wish I had better advice for you. I hope Petsmart can help, or at least get you hooked up with a vet. Since this has happened to you now, it's really important to start saving for a vet fund if you can. I'd love to see one of your hammocks because I'm actually looking for some for my babies. Post a photo of one, okay?
Added:LOL, we crossed our posts