It has been my experience that if the leaves are sagging, as opposed to the outer parts of the fronds curling down, then that is either over or under watering. If the leaves are still standing up but only the outer parts of the leaf fronds are curling down, then that is an early sign of over nutrient.
If you have strong nutrients in the soil, even in an organic setup, it is possible to get a nutrient surge when watering if the levels are just right. Its not enough to burn them but just enough of a surge when the water comes in and activates and mobilizes the elements in the soil, to give them "too big of a mouthful" initially, and cause them to show early signs of nute burn, but then as the soil dries out, the elements become locked back in place and the plants level back out.
This is more of an educated postulate than an actual tested fact.
