Dying leaves

Hi, I tried to Google something but couldnt find anything. I switched to flowering almost 2 week ago. After that on 2 plants leaves started to curve, become dark green and fall. Almost every new leaves that are growing are growing immedietly like that.

I really don't have much experience but nitrogen toxicity was the first thing that popped to mind. Just bumping your thread hoping more experienced growers will jump in and tell me I'm full of shit and give better advice.