Oh, I really loved this one! During a visit to hospital (for the school) two years ago I met a girl with aphasia and it was really really confusing even when I had studied about it. I can't even imagine what it must be to be the affected one and I think you did a wonderful job with your Harry here. I, also, loved your Severus, still snarky and all, but helping Harry and even speaking in a special way for him.
And I loved the "Sev",I mean, I really like it when Harry calls Severus that, but I wouldn't dream of a IC Snape who allows that or a IC Harry who dares, except here. Here it's perfectly justified, after all.