no... it is a natural thing for plants to do in the heat... mine have done it all my life.

If plants loose more water from their leaves than they can replace those leaves will wilt. Heat can do that and that is one of the reasons your soil should be well covered with a mulch, the mulch will help modify soil temperatures so the plant does not loose as much water and won't tend to wilt as much.
There are a number of other things to cause plants to wilt in the heat however, insects are one, disease is another.

As long as all the plants wilt, and they all recover in the cooer evening temperatures, then I would write the wilting off to heat stress and ignore it. If it seems excessive, and you get worried, then you CAN spray the plants with water and see if that will perk them up - more from the cooling effect than from the added water. As kimmsr said, the more you can keep the soil moist and cool, the less stressed your plants will be, and the less likely to wilt from too much heat and water loss. It IS scarey to see all your precious plants lying there, limp on the ground, though!!!