Weeping leaves on hot day?

Can anyone explain to me a phenomenon that seems to happen at the end of a really hot day?

Im growin right out back of my house, so i can check the plants frequently for problems. So i check the plants around 6 n theyre fine. I go back around 7 or 8... and to say i was surprised would b an understatement. The larger plants (2-3 ft.) literally look like they gave up on life - the leaves just dropped. Not off, just down like they went limp. By the morning theyre alive and perky again.

Its not like "o, the leaves bent down a little", no theyre literally vertical, and parallel to the main stem.

I wouldnt believe a plant could move that much over night if i didnt see it myself.

any insight appreciated.
peace

have they had a drink in awhile?

ya. light rainstorm night before. and nute-water mid day. (it was mad hot)

Also, a deer or somethin ate a small lower branch off one of the plants in question, and the plant "bled" water drops. i'm assuming that means the plant is hydrated. Its not causing the weep, cuz deer eat em all too often .

I was wondering if this "weep" is even a problem. if not, what does it mean?