I want to thank you all for the input! In here I have found several helpful advices, some of which I already do (write down plans and info in text docs, organized into folders for example, using my own flaws in characters)...but that leads to a rather important discovery after reading your posts: I really shouldn't be so worried. 

While disorders and memory loss are embarrassing in person, it doesn't always affect my writing or whether I'm willing to just buckle down and have a good time. I wasn't really feeling sorry for myself (way too used to it for that), but I'd say my life has kinda revolved around my problems to the point I felt they were the basis of my world...not necessarily! I've noticed that I'm far more composed on here than real life and I should take advantage of that based on the whole reason I want to do this again: it's fun and relaxing. It should help me in more ways than one to let the writing beast loose despite struggles.

You guys reminded me this isn't some sort of test to prepare for, you guys just "do it" for the most part. It's a beloved second nature, and I'd like to get to that point too. So thanks again. Maybe I wasn't really fishing just for writing advice, but also fishing for a confidence booster: last night I tried to get started but the thought of making a char or something made me nervous. Will people hate me, or will they hate what I write? Well, it's two separate things isn't it. And like I realized, it's not a test or a big deal. It's okay. The practice will help that anxiety at the very least.

I hope that others can find some useful tips about writing in this thread as well. So if anyone else has thoughts, feel free.