unusual behaviour of my Star Tortoise (please help)

by Jo
(Malaysia )

Hello, I have a 5 year old Star Tortoise, and he hasn't been eating lately. He hasn't been moving around much too and he has never been this inactive. He seems to hide in his shell, sleeping most of the time. Oh and I've noticed that he hasn't been pooping lately too. This happened just a few days ago, and I'm wondering if it's indigestion or if I have overfed him. This may sound absurd, but is it possible that he may be depressed of a recent death of another pet(a small chicken) of mine? They were seriously quite close.

Can you please tell me what wrong's with my tortoise? Would really appreciate it.
Thank you so much.