Depression?

by Ryan
(England)

my 5 year old hermanns tortoise seems kind of depressed right now. he dosnt eat as much and tends to sit around or pace around slowly. before when i let him run around outside or inside he was pretty fast and would do weird things like try and chase my cat. he dosnt sleep any more than he used to - hes just a lot less active.

the only thing that i think could have trigged this, is that he cant go outside anymore (its way too cold) but ive never had this problem the last 4 winters ive had him. besides i still let him walk around the house, which he normally loves to do.
what could of caused this, and how can i fix it?
thanks in advance.