I have a rat (Emil) that is 3 years old. Emil has started acting strange, when she goes to eat she will either fall backwards or to the side as well she seems to struggle walking and climbing. She was the most aggressive rat we have but has since became very tame and less alert about her surroundings. This has gone on for about 4 weeks and now she is losing weight like crazy. What could be wrong? I know she is getting up there in age and wonder if this is something unfixable.