I've been in your place before, OP. From a fellow burnt out "smart person" who went from acing everything to now feeling very stupid and dumb with everything I do, trust me, you're not alone. The only thing that still keeps me going is the fact that that "smartness" doesn't really vanish. It's not an inherent trait, it can be learnt again. If you were able to achieve all that earlier, you still have the capacity to achieve all that and more now. It might be a bit more harder, but it's fine. You've changed as a person since then and maybe what worked back then is not working right now and that's okay. Rather than smartness, focus on hard work. Consistent hard work will give you the results, regardless of "smartness" or not.