Should I e-mail my professor after completely blanking on my final exam?
Sending an email to your professor is fine. It also sounds as if you are doing your best, understand the course well enough to at least pass, and are not making excuses or asking for undue favors. Your professor will know this as well and will be much more willing to help you out because of that.

As @DreamConspiracy points out, I'd state more clearly what you hope to achieve by sending this email to your professor. This might be something like: "Is there any way for me to retake the exam in case I get a failing grade?"

If you are worried about losing financial aid, maybe you want to also contact the financial aid office. How are your ADHD, Anxiety and OCD implemented in your aid package?