well im not botanist and i only started my first grow yesterday. but i think ive heard that when some plants dont have enough water, they can kinda curl up. cause if you think about it, they pull water through their roots, up the stem and then it transpires out the leaves. so if it doesnt have enough water, it would curl up so that less of the leaf was showing. cause how much water gets transpired through a leaf has to be proportional to the area of the leaf. so less are exposed to sun (ie curling up) less water is transpired. less water transpired = less water lost by plant. so i think its a water conservation mechanism. so it needs more water. but like i said, i have zero experience so i could be wrong. good luck though man