Believe it or not, it sounds like your jade plant
is too wet. This is how mine have reacted when they sit in soil that has been wet or damp for a while - they really prefer to dry out between waterings.
You will probably lose those lower leaves, but you might also get new growth from the area where they fall off. If not, and the stems get too leggy for you likes, you can cut the upper portion of the stem off and replant that, after you let it callus over for a day. If you decide to do that, you would probably get new growth from the stems that remain, also. This is happening with a large jade I have right now.
Here is link to my thread about it, though mine fell off for a different reason, I do think the entire plant
was also too wet at the same time. my poor jade