Rot at the base. Do the opposite of watering: let it dry out fully, check the pot drains, and inspect the base for brown mush. This is why you always feel the mix before reacting to a droop.
What’s causing it
Thirst (dry potting mix)
How to tell
The soil is bone dry and the whole plant has gone limp. It perks back up within hours of a good drink, often with shriveled pearls beforehand.
The fix
Water thoroughly (for a String of pearls that’s usually every 11 to 17 days in summer), and the leaves should recover the same day.
Cold, wet roots
How to tell
It’s sitting near a cold window or an AC vent, and the soil is damp at the same time. The combination of cold and wet is what actually stresses this plant, not the cold alone.
The fix
Move it somewhere with steadier temperatures and let the soil dry fully before the next watering. Cold plus wet roots is what tips this plant into trouble.
Recently moved or repotted
How to tell
It started drooping right after a repot, purchase, or move. The disturbed, slow-to-recover roots on this plant can’t take up water properly for a while.
The fix
This is transplant shock. Keep it dry for a week or two rather than watering to ‘help it settle’: extra water on a stressed, slow-rooting plant like this does more harm than good.
Too much heat or sun
How to tell
It wilts in the heat of the afternoon but recovers by evening.
The fix
Shift it out of direct midday sun. A temporary wilt in heat is the plant conserving water.
Prevention
Before watering, check that the pot drains freely and never sits in standing water. If the mix is still damp, wait and check again.