I am glad Rocky is recovering after that! An 11 day stay in a vets office for a bird (especially if Rocky has been in the same home his whole life) could be a very traumatizing experience. They don't understand that being left in a strange environment with strange people was in their best interest. They just feel as though they've been abandoned by who they love and trust at a time where they were sick and venerable. You did everything right of course, but there will likely be some trust lost and a need to rebuild that trust with him. Plus, it sounds like he is still in the recovery process, and they tend to be quieter when not feeling well. Is he on any medications still? Some medications can affect balance. Does the vet know he's off balance, and if so, what does he/she have to say? If not, you need to let the vet know as soon as possible.
If Rocky suffered a stroke, one side of his body would be notably affected, just like when a human suffers a stroke. One of my moms bird had a stroke several years ago, and while there was some initial improvements in mobility, the wing is permanently affected and the foot permanently "curled" on the side of his body the stroke damaged. I would imagine if he showed symptoms of a stroke at the vets, they would have investigated. If he is showing these kind of symptoms of reduced mobility on one side of his body and did so after coming home, you need to let the vet know ASAP.
