I reckon too much Nitrogen but I'm no expert. You usually get really dark leaves when there's too much N
Curling and clawing first should be distinguished from droopiness. If the leaves are droopy and flex very easily than your plant is suffering from extreme over-watering or extreme under-watering.
Clawing and curling is distinctly different from droopiness. The leaves will want to “spring back” to their curled/clawed state even if you move them around in your hand. Often times they are accompanied by a “cup” shape formed by the leaves.
Curling can be caused by a number of factors including, over fertilization (this is accompanied by necrosis and yellowing starting at the tips of the leaves working their way inward). Extremely high heat can cause the plants leaves to curl under and with scattered necrosis and yellowing of the leaves. Excessive light exposure is related and can cause similar problems (like a plant getting too close to your HID lighting). If you Foliar feed in a hot environment, close to HID lighting, it can cause small burns on your plants and result in a weird wavy looking leaf that claws downard or upwards in random directions.
Other issues that can cause clawing are related to PH and nutrient bio availability. PH fluctuations can affect the availability of nutrients and cause the plants cells to grow atypically resulting in cupped shaped leaves that curl downwards. Other Nutrient deficiencies, either caused by a lack of concentration in the soil or nutrient lock out from bad PH, can cause the leaves to curl either upwards or downwards. Excessive Nitrogen or lack of Nitrogen can cause N-clawing, simply referring to Nitrogen-clawing. Its normal for the small sugar leaves to N-claw a little bit assuming you’ve reached peak saturation and nutrient availability.
Its important to take note of the Other symptoms that accompany the clawing to make a good determination of the problem.