Watering incorrectly. It might have issues continually now. BUT you could make it comeback. Just make sure you THOROUGHLY water every inch of the pot. THEN let it dry out it might take 5-8days. MAKE SURE it's light as air when you lift the pot this will tell you if it's dry. KEEP doing this and it might make a comeback although not always. If it does comeback it should be within a week or two. Too dry is better then too wet. Can't breathe when it's small and wet.