Answer: You may be overwatering it. Cacti in pots generally need watering about once a month. Water slowly and allow the water to drain out the bottom of the pot, but don't let water stand in the saucer. Also, what type of soil is it planted in? Regular potting soil is generally too rich/moist. You might want to try repotting it in a potting mix formulated for cacti if it's in regular soil. Cacti don't like wet roots and a typical response to too much moisture over time would be to get "droopy," but the plant is actually rotting.
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