My rat is acting very lethargic and seems to have lost cordination

Question
I have a male rat(not neutered) that has suddenly become very lethargic and has lost a lot of cordination.  He had a cage mate that passed away about a month and a half ago.  I did not get a chance to replace the cage mate until a yesterday.  He has seemed very lethargic since his cage mate died, but yesterday when I introduced the new rat he took no interest at all.  When I finally put them together in their cage, he was trying to climb up to a shelf where the food bowl is and fell off.  Since then he has been acting somewhat dazed and has not been very active.  I can't see any external injuries, so I'm not sure if he just fell and hurt himself or if something more is going on.  He is about 2 years old.  Is this a common problem in older rats?

Answer
It can be a problem caused by age, but because it only started happening after the fall it may be something worse.  Older rats often lose some of their senses including sight or hearing, but they normally keep their balance pretty well.

Since the behaviour occurred only after the fall, it is very possible that he suffered a head injury.  If he is still eating normally and can walk properly you can just watch him for a few days to see if he gets any better or worse.  If he is lethargic for more than a few hours, walks strangely or not at all, tilts his head to the side, or shows lack of interest in food, I would take him to the vet immediately.

It is possible that his symptoms and the fall were merely a coincidence as well.  He may be suffering from a brain tumor or inner ear infection, the latter being curable with antibiotics.  Just keep an eye on him for now and if he doesn't get any better within 24 hours or he gets worse, make an appointment with your vet.

Good luck!