My Christmas cactus is drooping. I have it setting in a window so it can get sunlight (there is a shade on the window if that matters). I think I water it pretty regularly, but I'm always afraid of overwatering a plant because I have done many in over the years by doing this. It just looks droopy and is starting to look a bit discolored, like a lighter green on the ends. I think it needs water now, but how often should I be watering this plant?