My plants are wilting but my medium is wet, what is wrong?

Very bad root rot can cause this. If you are able to look at the roots, then you can see if they are white or brown. If they are brown then it is root rot. But if the roots look white or slimy then you have either Fusarium disease which in most cases is like a blood clot that forms at the base of the plant & does not allow it to drink or you have Pithium which is also a root bound disease that looks like slimy boogers on the root system that does not allow the plant to drink.

Both of these diseases will also cause the plant to wilt during the day (or when the light is on) but at night (or when the light is off) the plants will stand back up. Both Fusarium & Pithium are known for destroying entire crops in 1 or 2 days. Root rot is easy to fix with 35% food grade hydrogen peroxide at 1 oz per gallon ran through the root system as a flush. Fusarium & Pithium you can try hydrogen peroxide but you will more than likely lose everything that gets it. The best thing to do for Fusarium & Pithium is not to get it with preventive measures like not taking air in from outside for your garden & always making sure keep your garden sterile (do not come home & go into your garden without showering & changing). You can start off with root rot & get Fusarium & Pithium.