curly leaves??

Hi,can anyone tell me why an otherwise healthy looking plant 4 weeks into flowering,would start to curl up and droop on her fan leaves??help??

Salt buildup in soil
pH of soil has dropped over time because of fertilizer use
Rootbound
Could be a few things.

if its root bound it will stretch badly and b poo not die!

You need to post pics for better answers.
A rootbound plant will be sickly, be hard to water properly, give you crap for bud, and be prone to diseases.
Indirectly it can die of whatever diseases it might get, just do your plants a favor by giving them the right sized pots.