Maybe its under water? I mean if your soil is still wet after a week you may have a problem with bad drainage. I think you need to water more then that... But if the soil is not telling you it needs it hrmmm..?
Yeah I was watering about once every two days because of my container being too small. But about 2-4 days seems good. If its as dry as you say it needs water and is drooping because of that.
stumpsx2 idea is good and should give you a good idea of when it needs to be watered. If its dry that far down it needs some water.
From the picture I just think that the plant stretched so much that the bottom leaves just don't have enough light to stay alive.. since the topmost leaves don't seem to be all that droopy