I've been prescribed Adderall for years. It's great, but it can cause a real crash if you run out or skip a few days. You just feel like you wanna sleeeeeeeeeeeep
And then when you start taking it again, you get all hyper around noon, your heart starts racing, and you can't get your mind off of things. Which I guess is supposed to help with concentration, but for God's sake, don't let yourself get distracted or start daydreaming or you'll be still doing it two hours later. It's hard to just let things go.
But after a few days back on it, it all evens out and feels normal.