I use Fox Farms products and I not only follow the instructions on the containers but I also use both the Big Bloom and Tiger Bloom at the same time.
 
As it says on the Big Bloom at first sign of flowering follow the heavy feeding instructions, ½ cup per gallon, which I did and I also added the 3 teaspoon feeding instructions on the Tiger Bloom. In addition I added one drop of Super Thrive.
 
After that I follow the every watering solution directions, again using both Big Bloom and Tiger Bloom and also one drop of SuperThrive. I have never experienced any burning and I have never had even the slightest drooping occur.
 
You plant looks like it is suffering from over watering even though you say you know it has not been over watered.
 
I doubt it is a nute lockout problem because there would have been other signs that would clearly have pointed to that possibility.
 
When did you take the picture? Was it right after your lights came on for the day? Plants will droop/rest at night and in the morning can appear to be droopy but within a fairly short time will again stand up as they absorb light energy.
 
What is the temperature in your grow area? While I could see no sign of heat stress in your picture it could be possible that your plant is in the very early stages of heat stress and the leaves have not yet shown it as in necrotic spotting/drying/browning but that could cause the droop.
 
What sort of soil are you using? Is it light and breathes easily or is it tight packed and hard and unable to breath well? If so your plant may have reached a point where its needs cannot be met by the soil.
 
I could not see the size of the pot you are using but if you are using a pot that is too small in size wilting/drooping is very common when a root-bound condition occurs. As roots build up what little soil is in the pot is compacted and the soil cannot retain enough moisture. When you water you get more runoff than retained moisture and very soon your plant is starved for moisture.
 
If possible fill everyone in on as many different details as you possibly can, even if you feel they may not possibly be part of the problem and then with some lucky someone can hit the nail on the head and tell you what the problem is and what to do about it.