I've only done 1 grow , 18 months ago or so, just moved and got a bigger place and a better cabinet.
What kind of light are you using? {edit} to cause a heat problem? I used a 400w and the heat was vented out a wall, have you got proper venting? Or are you using the A/C to cool the room? The plants obviously need fresh air.{edit}
My plants did this last time I grew, I was using a high N for most of the flowering, I noticed that the leaves went yellow, only the fan leaves though and mine went from bottom to top.
Anyways, to cut a long story short, only the large fan leaves were affected and at the end after the cure etc, all was fine.
Although if a more experienced grower would care to enlighten us both that would be great.

To sum up: My plants were fine when this happened. 4/4 had it and 4/4 lived till I cut them and 4/4 smoked and tasted ok