Hopefully you will not need to give up your regular Jazzercise class since it has worked for you this past year. Most likely you have "tweaked" a ligament or muscle that attaches to the knee. Even seasoned athletes can get a strain and subsequent inflammation that causes pain. Your knee is saying "rest me", so you need to listen. No Jazzercise or vigorous exercise until the pain is gone. Apply ice three to four times daily for 10 minutes, and let the inflammation quiet down. After you are pain free, do a few of the Jazzercise moves at home and see how you do. Continue with incremental Jazzercise moves each day until you are ready to go back to class. If you experience pain at any time, it is time to visit your doctor for a proper evaluation.
Studies have shown that regular walking, biking, dancing, or using the treadmill are all good for maintaining health, fitness and longevity. Your body will tell you if you can continue with your Jazzercise classes or need to seek out another form of exercise.