Succulents store water in their tissue. That's what makes them succulent plants. They use the stored water to survive long, dry periods. Since succulents, as a general rule, grow in dry places, they take up water through their roots very quickly and efficiently. On the other hand, they cannot quickly remove excess water. This works fine in the wild, but in cultivation, people can give succulents more water than they need. This is common, and cultivated plants often look plump and happy compared to their wild counterparts.
But the real problems start when people do not just give their succulents more water than they need, but more water than they can handle. This is overwatering. When a succulent is overwatered, it swells more and more, and often the stem becomes so saturated that it splits open in one or more places. While a succulent can usually recover, overwatering can also cause rot, especially when combined with cold temperatures. Sometimes only the roots rot, but the whole plant often turns mushy.
Treatment
The first thing to do with an overwatered succulent is to stop watering it. In most cases, repotting would also be a good idea. When the plant is out of the pot, let it dry for a week or two, then repot it. If the plant body has split anywhere, the damage is permanent, and you can only let it scar over. If the plant has started to rot, saving it depends on how far the rot has set in.
Source: succulentguide.com
Links
- Succupedia: Browse succulents by Scientific Name, Common Name, Genus, Family, USDA Hardiness Zone, Origin, or cacti by Genus