I tend to stick to lower impact stuff such as yoga and Zumba (Zumba is quite good if you want a cardio work out by the way).
The usual advice is that you shouldn’t just pitch straight into the whole thing if you are starting something new, no matter how fit you are, but build up slowly to reduce the risk of injury.
If you are feeling it already, I would stop now and see how you feel tomorrow. If you feel very sore and stiff tomorrow then you will need to break for a few days until the pain goes away. A chap I used to know at work who was really into gym workouts used this rule, because when you feel that pain it means you have torn some muscle fibres. These will heal even stronger than before, but there is no point in disrupting the healing process by tearing them again when they are not ready for it.
Hope this helps!