Hibiscus in the winter indoors will lose their leaves. They are fighting to go into dormancy. You can try to keep it from going dormant by providing more light and keeping it a little warmer (though it will not look as good as it does in the summer while you have it indoors) or you can just let it go into dormancy.

If you want to allow it to go dormant, place it in a cool, dark place (basements and closets work well). It will lose all its leaves and look dead, but it is fine. Water it once a month - no more than that as it does not need much water in dormancy. In the spring, you can bring it back out and resume normal care.