This is a very good and tricky question. I think that we have to take a step back here. The first question you want to ask yourself is -- "has my disorder affected my academics or work performance so much so that it is reflected in my grades or performance evaluations?"
Academics -- if your disorder affected your Academics, then I would definitely bring it up in the optional essay. I would not necessarily use it as the crux of a greatest challenge essay. "greatest challenge" essays are usually reserved for a leadership experience and particularly a work leadership experience.
Work performance -- if your disorder affected your work performance, and this is to be reflected in your recommendations, I would bring it up in the optional essays well.
However, I want you to carefully consider whether or not you should bring it up at all. Having only recently overcome your disorder, there are going to be a few doubts in the admissions committee reader's mind. They are going to wonder if you are fit for duty, so to speak. Also, if you do bring it up in the optional essay, you better be prepared to tell them that you will supply a doctors note attesting to your condition.
If you have been a successful employee, in whatever capacity, I would suggest that you do not bring up. It is too recent of an event to demonstrate a history of overcoming it. The trick with any challenge essay is to demonstrate not only "lessons learned", but that you have truly learned lessons by having the opportunity to employ them and generate a substantial result. If this only recently happened, and that history of showing that you have utilized the lessons learned to some effect simply not there. So I recommend avoiding it altogether.
I really hope that this helps in your decision to use it as part of your application.
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