The most common reason for a Christmas cactus to droop is due to improper watering. Make sure you are giving the plant the right amount of water at the right time. Too much water can cause the leaves to droop, while too little water can cause the plant to wilt. If the plant is not receiving enough light, it may also droop. Make sure to keep the plant in a bright area, but not in direct sunlight. Additionally, if the temperature is too cold or too hot, the plant may also droop.