Wow. How will this affect him as he grows up ?(don't feel you have to answer that if you're not ready to talk about it yet). It's good that you were able to spot it early so the pyshio could start so soon.
Have you thought about starting a diary to record his progress. Maybe it could help when you're feeling down to look back and see the improvement being made. Also have you spoken with the physio or Dr about getting in touch with other families with children with FBS. Danielle's physio has but us in touch with other families and I have found this useful.

P.s Danielle's was a birth injury that paralysed her arm. She can probably use about 40% of it now. Not quite the same as what you're going through.