Hey Blue. I'm sorry this concern has been raised by your manager. I imagine it doesn't feel good to hear that feedback.

I think maybe though there are two separate things going on. You've had some issues either up or down one way or the other for quite a while now. Throughout all of those you have reported increased difficulty concentrating. I imagine the culmination of all of those periods resulted in less work production. I know there were times you mentioned your coworkers even noticed something was up. You seemed dialed into all sort of things other than work at the time, so maybe if you get better control through your recent med changes, things will improve? I think you have every reason to be hopeful for that.

I think those issues adding up is probably different from the normal level of distraction you experience due to the attention deficit. Lots of managers work with those with that diagnosis and they are trained to make accommodations in many cases.

At this point it seems likely to me that your coworkers sense something is amiss. Could you tell your manager you have attention deficit and are working to iron out a few issues with it? That way you wouldn't need to expose everything, but maybe he could have greater compassion for your needs. You're incredibly intelligent and I imagine you to be quite an asset to any team. Hang in there!