I think you couldn't sleep because the quetiapine would have helped with it, so when you went back to risperidone your body noticed it was missing. Sometimes its a psychosomatic kind of approach, as your brain is like "hey there's something different going on here" and you need to get accustomed to being on your original risperidone. Quetiapine is a strong drug, but I take it as an antipsychotic mostly but it does help with my mood. I took additional Zyprexa for a while and when I stopped, I went into withdrawal like I was sweating like a maniac for months after while trying to come off it. Goes to show you get hooked on these drugs.