My zucc's did the same, a couple of times. I have had no luck with mine this year. First one plant had a worm
(assuming squash borer or close relative) I have a hard time even touching them - let alone trying to figure out what it is. I found the hole cut it out and actually repaired the plant - It is still growing and just now getting zucc's on it. I had to baby it along. The other was a Black beauty plant it looked fabulous - I mean the best plant ever - it was in a raised bed and everything in the bed was doing well. Then one day it was wilted. I though the Fl heat got to it. I then watered it. Well it never improved.
It just got worse and worse, I could never find a worm hole. I (after reading) assumed it was root rot. When I pulled it I searched it all over for worms and there was nothing, - I guess it was over watered. No fungus or anything remotely fungal on it that I, a beginner could tell. So I guess it got too much water somehow and the drainage was bad. Sometimes I just can't fgure it out.
It was a great raised bed, good drainage as far as other plants go, mulched with straw, then it just died. So I hope you can salvage yours - this is once where the worm may be he lessor of two evils. Good Luck!
I love this! - There can be no other occupation like gardening in which, if you were to creep up behind someone at their work, you would find them smiling.