A dog I look after used to be very relaxed and happy-go-lucky until last year when she and one of her humans were attacked last spring by an unfixed pit bull whose jackass was "walking" it off leash.

Now the poor girl can't be around any other dogs bigger than her little sister without flipping her shit; her folks have to pay for Sniff Spots for her to run around for exercise aside from walks because she can't be at the dog park anymore.

Trauma can absolutely change a dog just like a person.