Plant was fine in the morning, come back and a lot of the leaves were limp almost as if we had it covered in the sun and they looked like they were cooked, kind of like cooked spinach.. We have been covering the pot with plastic for warmth..nights have been chilly, which we remove in the morning (lots of moisture in the bag and on the plants). It is in a planter and we water from the bottom. I've grown tomatoes for a long time and have never had this problem..living in the desert now. I'm thinking we should leave the plastic off since night time temperatures are in the 40's now
It sounds like the leaves were actually heated or died from the excess moisture that formed on the plants leaves.
Tomatoes can tolerate temperatures that drop to 55 degrees F.
You may want to use a cloth sheet to cover the plants if the need arises instead of plastic.