yellow leaves usually follow a period of drought
Lets say you have the plant inside, after it has been outside all summer.
Now with it in lower light, lower humidity than it likes, some leaves will drop naturally over the course of the winter. This is because the plant is not able to support all the leaves it had when everything was going good. When the plant sustains a dry spell or is put in a cool room it will react by dropping a bunch of leaves at once.
Check to make sure it is not sitting in water.
Water should not run straight through, if it does chances are the root ball has dry pockets and is not staying evenly moist.
Make sure the plant is getting 4-6 hours of bright light a day.
Don't overreact and drown the poor thing though.