How have you been watering it? Your plant could be stressed due to improper watering. You should only water your jade plant when the top of soil is just dry to the touch. If you have been over-watering your jade (indicator: damp soggy soil) then it is possible your jade has root rot - the following article will explain how to treat root rot:
Another possibility is a nutritional issue. How have you been fertilizing your jade? You should fertilize your jade plant about once every six months using a balanced water soluble fertilizer.