I have recently read more up on PSD dogs there is a good book that talks about them called Healing Hands.
To have a service dog you have to be impaired a mental illness is an impairment if this person can not function on a minimal level because of their illness.
Emotional support dogs are dogs that provide companionship,affection, comfort and are not trained to in task work. They do not have the public access that PSD dogs to under the ADA. They are well trained pets that are emotionally in tuned to their owners but from what I have read to have benefits vs a pet dog.
"However, their owners are afforded privileges through a Federal grant which allows them to keep the dog in most types of housing, even when there is a “no pets” policy. The Air Carrier Access Act provides policies that permit a person with a disability to travel with a prescribed emotional support animal so long as they have appropriate documentation and the animal is not a danger to or interferes with others."
Emotional Support Dog
As for PSD dogs they are trained to work and perform a task for the person. There are various tasks that they can perform either be in at home or in the public situation. These dogs have the public service hours training and can work in a public situation comfortably and reliably. Tasks that a PSD dog can provide stability if a person gets dizzy or after an episode, waking a person up if need be, blocking a person from danger, if they become disoriented in public leading them to a designated person or safe zone, before an episode occurs they can interupt the person before it happens.
It is interesting when you read about PSD dogs because they do different tasks that a guide dog can do (guiding the person or blocking them from danger), some things a hearing dog can do (alerting or signaling the person if they are sleeping heavily because of the meds they are on), what a mobility dog can do (bracing a person or stability support) etc..
When you look at the difference between Emotional Support Dog and a PSD dog you are looking for trained behaviors vs natural behaviors.
Upon reading about the difference I found an interesting statement and it said this is what the courts will ask.
1. is the behavior the dog is doing trained or natural
2. it must migrate the person's disability
3. it must be needed by that handler
After reading different websites and books this is where I am at with the differences.