There is a saying "If it hurts you are doing it properly" - a favoutire saying by ultra fit gym instructors!
But when does post workout ache become uneccessary pain?
I did a spinning class on Saturday morning and still cant walk properly, surely this is not "a good pain" and I have over done it??
As Pixie says, never do exercise classes 'cold' always do warm up exercises then follow with stretches - plus if you were previously not doing any exercisr you have used muscles that have lain dormant.