Do Dogs Also Suffer Emotional Trauma?

Hello guys.

My friend had 3 big alsatian dogs. Unfortunately 2 of them died due to illness. But the third one that survived has not been the same since losing it's other 2 friends cos he witnessed their deaths in the cage. Doctors say it could have affected him mentally.

Honestly this once fierce guard dog has become a shadow of it's former self. It just sits around the house all day moping and doing nothing. It never barks anymore. A total stranger can come into the compound without any fear even though we don't cage him anymore. The most shocking part is that the stranger can shout at him and he'll RUN AWAY inside his own compound.

It grieves me to see him like this. Is there anything we can do for him now? Cos basically we're just taking care of him now as an aged friend.

That's him in the compound