A larger dog can be trained to help a person that hits themselves during a meltdown. There is a Youtube video of a dog doing this!
My ESA is just a rescue dog that i chose because she is people oriented and a breed that bonds with one person. She has only basic obedience training...sit, up, off, quiet, come, etc. I take her everywhere with me, doctor and dentist appointments, my lawyer, Starbucks, bank, etc.
I have agoraphobia and a little social anxiety, GAD, and chronic depression. With my Samantha, I am able to leave the apartment and talk to strangers.
How does she help? Just by being herself. I can focus on her when I am stressed, I can give the command to get into my lap so i can pet her (i use non verbal commands so people dont know i need her at that moment) I can use her as an excuse to leave a room or conversation without a reason, I just say she has to pee.
BUT, there are also times when she makes things more difficult. People will make unkind comments, give us dirty looks, sometimes Samantha gets overwhelmed herself and disobeys and gets hyper and barks.
But I would not have been able to leave a bad relationship and live on my own without her. We rescued each other.