lights. I don't think the fish see red light. Then you can look at them without scaring the daylights out of them. See if their gills are moving slowly.
Just shining a light on them can cause them to panic, swim quickly but randomly and even fatally clobber themselves on a tank side. I agree with Nika that they were probably resting/sleeping. Since fish don't have eyelids, it is hard for us to tell.
Their colors fade though. And they are as groggy when awakened as many of us. ;)
Small fish would naturally "roost" in plants. Sleeping on the bottom happens a lot, but they are more vulnerable to bottom foraging predators in nature and in aquaria with that cute little unidentified catfish.
When our kids were just tiny infants, they scared us because they were so still in their beds. We'd quietly as possible put a finger in front of their nostrils to see if there was any breath. Probably the loudest noise was our exhalation after finding out that they were ok. :)
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