Oooooh boy, yeah, that's more than likely what's causing it. I don't know much about the nature of the drug you were taking, but if it's a strong one and you were taking it in the normal to a greater than normal dosage, what you're feeling is pretty normal, if not a good thing. You DEFINITLEY need to get back to the doc. and talk about what's happening and how you're feeling, but no, you are not losing your mind or anything of that nature. What you're going through is withdrawal, and your brain needs time (quite possibly a lot of it) to adjust. Remember, this drug was messing with your brain chemistry, and it'll take a while to balance out again.

luck&love,
~muse