In trying to understand what is happening, the Maranta's leaves close at night...somewhat, to conserve moisture.
This suggests the leaves should not be drooping if its been given sufficient water. The leaves falling off suggests that is not the case--quite the opposite.
It does like sun....but not directly.
The closing of the leaves and opening the next morning suggests the light is correct and the moisture content is correct. A saucer of water might be put close to it to provide some moisture. Perhaps, some misting might be done too.
If that's not the case, then suspect one of the requirements is not being filled.

The straggly leaves are, however, suggested to be pruned out regularly.
You might, while it is still viable, take some cuttings and start some new plants...just in case.

Hi, thanks jerrycan for pointers, however, the leaves do not 'drop off', they only break off if forced to come back up to a horizontal position. I have the plant sitting on a pebble tray for humidity and I always ensure that the soil is consistently moist, not muddy. Could it be an issue with the water itself...I live in a rural area and have well water which is UV shocked, then filtered before reaching a faucet, and I try to make sure that the water has sat out for 24 hours before using it. All but the bottom 4 leaves still display normal prayer plant behavior, folding at night and opening in the day, although I believe that I briefly had it positioned where it received too much sun, as the colored spots on the leaves changed from brown to dark green, but I understand that this also occurs as the leaves mature. Any thoughts on the artificial lighting set-up?