I agree with Stinky's recommendation. I feed with a good bit of Nitrogen during veg, and every once in a while I'll have a plant that looks like it's suffering from N toxicity...dark green color, leaves curling under, giving a drooping look even though the leaves are still turgid.

I grow organically in soil, and usually after a flush or two, the foliage starts to recover. If it gets too bad, though, it can take a while to get back to normal.