Suddenly dead plants during flowering cycle

[KMH123]

First time grower here. I've been pretty successful raising my two female plants so far - a blue mystic and an unknown female, both from Nirvana seeds. Everything was going smoothly until the last few days when they unexpectedly died

Here are my details:
- Small grow tent
- MH light during vegetative stage, HPS during flowering
- Small intake and exhaust fans
- Regular old gardening soil with Fox Farm trio nutrients (I followed the feeding schedule pretty closely)

Both plants vegetated for about 5 weeks before I switched them to the flowering stage. I was 5 weeks into the flowering stage when they died. I didn't change what I was doing - only watered the soil when it got dry, 12/12 lighting schedule, etc. Does anyone have any ideas why they might have done this? Please let me know if I left out any details that would be necessary for the diagnosis.

Photos:
Here's what the healthy plants looked like a few days ago -

And here's what they look like now

 

[Ekko]

This happened on my very first grow. It was about 2 weeks old and just so healthy. The next day it looks like your plant.

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[Seaweed Farms]

What was your pH?

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[Seaweed Farms]

Did the gardening soil have any premixed nutes?

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[Twox]

What were your temps? Over 100? How big is your exhaust fan?
Does anyone in your home dislike your grow?

Looks like you suffered through a heat wave, did your Temps jump suddenly? If not I'm guessing somebody may have poisoned your grow.. That's some massive damage and if it happened that fast something changed in either the soil or your environment in a big way?

 

[MadScience]

Man, they got cooked somehow. Go back over what you fed them and check the room temp.

To do this kind of damage over a short period of time requires extreme maltreatment. Is it possible someone got into your grow room and dumped something on them? Maybe you miss-measured and accidentally juice them with 1000 ppm nutes? I've cooked a few plants over the years with nutes but I've never seen anything like this.