Rat snake - question

[COYS70]

Hi, I bought a 6ft rat snake last Aug 2012 and was told he was about 5 years old.he was a very placid snake who could be handled by all of us and the kids and always seemed happy and settled and very active in Viv. He was in a very small Viv in shop but spent a lot of the biggest one i could find. About the end of Dec he seemed to go off his food or going a lot longer than usual, and wouldn't take the medium rats he was having and started to only eat smalll mice. His skin looked like odd bits that looked like say scales had come off and I presumed he was going to shed. He became less active also not coming out from under his log hardly at all. He also struck and got hold of my partners thumb giving her a nasty bite and bruise. We didn't blame the snake for this and just wondered what was causing this. He had shed his skin about 2 days before getting him so guessed he was due. Since then he has not fed that well and rarely appears. Then yesterday he came out and had a long drink then I noticed him shedding and did so, which was great to watch. He then like nothing had happened seemed to be back to his old self going around whole Viv and very interested in us outside. Reading all the things you can about shedding explains everything about why he was as it all matches. What don't make since is that it seems like the process started months ago but has only just happened so am wondering if this can be normal or did I miss something. Am waiting until tomorrow to feed him so unsure of his appetite at the moment. Would be glad of some opinions. Thanks, Alan