start from the basics first,what is you're ph? if it's in the right range then you go to how are you growing them out?soil?hydro? if soil droopy plants can mean alot of things not enough watering or overwatering? in hydro droopy plants can be from foliar spraying with lights out will sometimes do this and is normal.do they perk up at all any time during the day or have they been like this constant? also have you moved them latey? maybe for a nute change? sometimes if you break off any roots this can happen also?