Answer: This sounds like the symptoms of overwatering. Have you changed the watering routine? Or have you moved the plant from a sunny, warm spot to a cooler, darker place, but kept watering it the same amount? This is the most common cause of the symptoms you describe. It's also possible the roots were damaged by too concentrated a fertilizer solution.
If the roots have rotted, there's little hope for recovery. Try removing the damaged foliage, cut back on water, and see what happens.
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