overwatering, you are giving too much water as it appears, decrease water volume and/or increase time between waterings.
best of luck growmie, the plant is looking good and healty apart from the droopyness.
(If they get droopy at night, it just means they are resting, doesn't mean anything else, doesnt mean thirst, doesnt mean unhealty, its just tiredness and then they set to rest, some plants do this, but not all.)