A couple of things are know to cause leaf curling like you describe. Sometimes sucking insects can do this. Unfurl some of the curled leaves and look for some tiny insects. If you see them, you may have found your culprit. Take one of the leaves into a garden center and show them, then ask for a recommendation.
Another possibility is exposure to herbicides, such as lawn weed killers. Have you used any lately? If so, it may be a case of accidental exposure. If so, the plant may recover, but there is nothing to do but wait.