They look like they need water but then they die.
Marigolds Go Limp and Die
It sounds like there is something going on with the soils. If the soils moisture is kept good they should be doing fine. Sometimes in strings of hot days the soils moisture gets depleted very quickly and the plants can get cooked pretty quickly. This scene that you describe can also be due to our dog or cat friends using the area as their toilet room. Or can be caused by something sprayed nearby that drifts over onto other plants unintentionally. It can also be caused by folks pouring out their drink or some other liquid upon the soils the plants are in or nearby that then leaches into the rot zone of the plants. I would keep an eye on your garden area and see if any of these issues reveal themselves. I have seen cases where a lawn care firm sprayed the neighboring lawn with something that drifted over onto an entire garden next door and killed the plants. They are licensed applicators and should not be letting this happen but unfortunately they do from time to time.