It is important to get a diagnosis from a professional when dealing with this condition, because there is a difference in treatment for your pet when dealing with this illness and stroke.
There is some difference in symptoms between PVS and stroke, the main ones are: with stroke there is usually no vomiting, and no flickering eye movement. Also with a stroke there is often paralysis on one side of the body, rather than an overall weakness as in PVS.
The good news is, that dogs can make a full recovery from both conditions, with some good herbal remedies, and a lot of love and care. (My 20 year old dog recently had a stroke, a bleed on the brain, and has recovered completely). If your pet has either condition, please give them time to recover before considering euthanasia.