why did this happen

Heat stress, using a 1k hps in cool tube, l still fought high temps, 110-120 but rh was dead on 65%, l grew pm all the time. And suffered through heat stress. Maybe raise light a few inches. And like other patron said let dry out, will make roots stronger. Other than temps they look great. Not your fault, lights fault. You have to roll with it, because hps will always run hot. Air conditioner helps, portable type. Hope your grow goes well.

My guess is too hot, too dry, and too much light. They look OK though.

Heat stress is part of the problem I would also say overwatering too thats why your leaves are drooping and the reason they are curling up at the edges is a clear sign of heat stress. I would suggest only watering when the medium is bone dry that way you know she is uptaking nutrients as she should be. You need to turn up your extraction fan and also increase your cold air intake if you can cooling the tent is hard but it can be done with the correct air circulation and extraction system. Just let them dry out and try cool the tent abit and you should be fine HPS lights are notorious for giving off alot of heat that's why most growers including myself will use cool air tubes on the bulbs which cools the bulbs its pretty much needed. Best of luck anyway my friend as soon as she drys up she will bounce back dont worry :)