My son was ADHD and was on Ritilin, too. It does have the opposite reaction with these kids.
When the fog rolled in for me, I thought I had Alzheimer's, too. I shed many a tear over it. I used to teach but now I can't remember the simplest things. But, I have found that since I know what is causing the problem and relaxed about it, my memory is better.
Stressing over it will not help it but it can make it worse. When I can't remember a word, instead of racking my brain, I just say I'll remember it later...and I do! It's like my brain shorts out. But, really try to relax about it. It is a cognitive memory problem caused by fibro. You are still an intelligent person but you have a health problem that is causing this. This is how I explain it to friends who ask me.
Good luck with the Adderall!