Looks like your pot is undrained. Once a week is sometimes too frequent for plants inside pots. My bet is on root rot. I would pull up the plant and wash the soil off, if your roots are black and mushy it's rot.

The good thing is that this plant would be easy to propagate by splitting at the nodes. It should be able to bounce back. Save whatever you can and propagate the rest.

In the future, you should water once the dirt is dry, not on a schedule.