Did you have scale, or other insignificant insect pests on the leaves? It could have been sooty mold. This mold eats the honeydew and sap that the insects leave, but don't eat the plant itself. If this is the case, the leaf drop was caused by the pests, not the mold.
Here's a pic:
Sooty mold is not a good sign, and shows that you have an insect problem. You can usually control the pests with neem oil, but if it is scale, you'll have to wipe them with alcohol, such as methylated spirit, or suffocate them with summer oil.
For now, I'd keep the plant in normal temperature, and give it a weak fertilizer solution, to encourage new growth. Keep it watered, and don't let it dry out. remove and dispose of the leaves that fell. When the plant puts out new leaves, watch it carefully, and treat pests as you find them. Don't use insecticidal soap on new leaves/growth. They may be damaged.