Too hot, too cold, too wet or too dry... All are possibilities as is having in same pot for a long time so there is no nutrition in the soil.

I'd echo Moongrower's response - more info needed, preferably with a photograph of the plant - and its container. How often do you water, are the leaves dry and crispy when they fall, or yellow and soggy. How long has it been in the same pot. Have you moved it recently to a new position? Or had extra heating on this year nearby?

Spider mites can also cause dropping. Look for a "dusty" look, almost microscopic yellow or tan stippling of the leaves. and/or super-finely woven webbing. Another test is to put a piece of white paper under the leaves, and sharply tap the leaves--you will see tiny rusty, yellow, or greenish specks running around on the paper if there are mites.