lethargy, but no other symptoms

Question
My, normally quite inquisitive, rat has recently become quite lethargic and uninterested in anything. She appears to still be eating and drinking, however when out of the cage does nothing but curl up under my jumper when normally she's up and about and all over the place. She doesn't appear to have any physical problems; no lumps or tilts, no strange discharges. When she moves, she moves quite slowly, but otherwise her mobility seems normal. I haven't changed the type of bedding I use nor given her any food different to normal. Her cage companion has perfectly normal behaviour and fine health. Apart from the behavioural change, nothing is different, but as it's not her normal behaviour I'm a little worried. Any suggestions?

Answer
Hi Kerry

How old is your rat?  Lethargy is a pretty big symptom that can match many ailments, from infection  to subclinical pneumonia.  I would bring her in to the vets for a good check up. She may be running a fever, which of course indicates illness too....the vet can palpate her abdomen to feel for any internal masses, feel the size and shape of both her liver and kidneys and listen to her heart beat and check for murmurs or other irregularities etc...