As succulents, jade plants don't need a lot of water, especially during the winter months. The symptoms you describe suggest that your plant isn't getting enough moisture into the plant. However, that could be because it has gotten too much moisture (enough to cause root rot), or because it is not getting enough moisture. Check the root system. Tip the plant on its side and slide it out of the pot. If it has a strong, solid root system, it must not be getting enough moisture. If the roots are soft or mushy, it may be overwatered.