Relevant anecdote: I used to do some programming for my job, and have an incredible vocabulary and am fluent in Chinese; I'm extremely "smart". But, sbout a year and a half ago, I was in a terrible motorcycle accident in which I was knocked off by an SUV and went into a coma, suffering a massive amount of neural damage to various areas all around my brain. Unfortunately, because of this brain damage, it is now incredibly difficult for me to learn some new things (specifically the logistical complexities involved in programming or advanced math/physics, for example). Also, my short-term memory is now awful. Many a time, in recent months, I've figured out how to do some kind of little software trick on my PC or phone, but then I'll forget how I did it, and have to spend hours re-learning it. Am I not "smart" anymore? Conclusion: sometimes how you appear and the things you say can't completely represent one's capabilities. "Smart" is a very broad, and possibly ambiguous term.
Side note: have you tried memory systems like Anki (spaced repetition)? As I've gotten older, it's been a godsend: my ability to pick up memory on the fly is shot, but Anki helps a lot. You're in a different, unfortunate situation, but it's worth a shot.
Ha! That's actually how I feel all the time. Learning something new is hard. If I don't use it I start to forget it. I do have two degrees: Engineering and computer science. I always thoguht this was normal. Maybe I'm stupid and never realized it? Iwonder...
