Sometimes you can find out the difference with some scientific method. Talk to your doctor about reducing or stopping the Risperdal briefly to see if the side effects improve. If they do, you'll know. If the doctor is unwilling to do that, maybe they'd consider switching to a different medication or prescribing a medication to help manage the side effects. Ideally they'd be willing to adjust the Risperdal and see if it's the cause. Symptoms could explain it too, but you'd want to see if you have other symptoms of your mood disorder than just restlessness.

Timeline can also be important. When did the restlessness start? Was it before the medication or after? Does it seem to be worse when you take your medicine or at other times? Do you find that you're bored or irritable? Do you find yourself more distracted? Some of these questions can help you and your doctor figure out if it's a side effect or a symptom.