What's the diagnosis on this certain Cannabis plant?

Over watering this type of plant will kill the roots that absorb water. With less roots available to take up water the plant will look wilted. Adding more water will accelerate the plants death. You should choose a soil type that it suits the plant and dries out quickly,especially if you tend to over water. Also, the soil will dry out quicker using clay pots over plastic. Let the soil dry out and if the plant is strong enough, it will send out new roots in search of water. Water again as soon as the soil is dry if the plant is still alive. In the mean time, start a couple more in case this one dies. And don't over fertilize, always use 1/2 the amount of what the label calls for.