I have a dog who definitely helps when I'm depressed. Im not sure about the opposite end of the moods though. I have been getting out of control and though she tries to be stubborn and hang around even if I'm irritated as soon as I'm angry she bolts which is best. If I can calm down enough to take a minute to pet her though then she definitely grounds me a bit. When I'm depressed I spend a lot of time petting her and cuddling(she is a lovebug too but 40lbs) its something to focus on other than misery and unlike my family she doesn't care what I say and only tries to make me feel better and can cuddle for much longer than my children!