i have a 12-14 week old male opossum who has almost spontaneously lost the strength and mobility of his rear end he can still move and grip with them yet doesnt he seems to just crawl on his stomach and back over his back legs when he does go forward he keeps his hands flat and stretched out his tail also seems to be more tense than usual and he seems to be more nervous than before his sister stays with him in the same cage yet is fine please help me