The wilting of a Christmas cactus is most commonly caused by improper watering—either overwatering or underwatering. Overwatering leads to root rot, which prevents the roots from absorbing water properly, causing the leaves to wilt, yellow, and possibly drop. On the other hand, underwatering causes the plant to become dehydrated, leading to limp, droopy leaves as well. Other potential causes include:

• Salt accumulation in the soil, which can harm the plant's roots.
• Too much direct sunlight, which can scorch leaves and make them droop.
• Temperature fluctuations or exposure to drafts, which stress the plant and cause wilting.
• Pest infestations, such as mealybugs or spider mites, which weaken the plant.

To revive a wilting Christmas cactus, diagnose the cause carefully:

• If overwatered, let the soil dry out, and if roots show rot, repot in fresh, well-draining cactus or succulent mix.
• If underwatered, soak the soil evenly, letting excess water drain.
• Move the plant to bright but indirect light and maintain stable temperatures.
• Check for pests and treat if necessary.

The Christmas cactus prefers humid, tropical-like conditions and does not tolerate soggy soil or drought well, so balanced watering and proper lighting are key to preventing wilting.