I just spent some time trying to find the answer to the wilting thing. I had it happen to a perfectly healthy veg plant a couple years ago. One day it looked like it needed water even though the pot still had some weight to it. I watered it and the next day it had basically died - nothing but collapsed leaves and branches drooping from the central stem. It dried up pure green.
I found a lot of posts from hydro guys and I never found anyone who had "the" answer. But there is also info from soil growers raising peppers and other veggies. One day they look a bit weak, the next day they're dead as a doornail.
One clue - it has to be a vascular problem. The whole system stops moving, as if you had cut the roots off. There are a couple of fungal diseases but they don't affect the plant abruptly like this does. I doubt they're the cause.
Something simply shuts down the whole pump/suction/valve system. There are pests that can infect that, but again, they move more slowly. This is sudden and fatal.