Quite a similar experience to me. After a change of meds I had a bought of intense disphoria and anxiety which I (perhaps falsely) attributed to the meds after 9 years of use and misuse (insufflation etc). I stopped cold turkey until my special authorization expired and haven't used them since. It is a relief in some ways that my overall as methylphenidate is quite hard on the heart and addictive, so it got me through the quitting phase. I've found other ways to get by with my ADHD; diet, sleep, caffeine, environment etc. Its possible the meds had already helped to establish the patterns of concentration too.