Do pups have a 'play dead' instinct?

[TJ's Rodent Ranch]

To start, I have a female (WD40) and male (Frank) with six, 6 week-old pups. I've been figuring out a way to keep breeding pairs bonded while they have a three month break from litters. How I do it, is by putting in a divider when the female is about to give birth to her second litter. 
This process requires the female and male pups to separate, and go with their mom and dad. (obviously, males with dad, females with mom) so they're always part of the divided process. 

Anyway, so I was doing this today since the pups had reached an age that they needed to be separated so they didn't make more, and something very strange happened when I was arranging the tank. It's a very simple divider so it's not hard or super disruptive to put in, but when I separated them, and finally got them onto their proper sides, in the only way I can describe it, the babies started shutting down. Both WD40 and Frank were both very active, but the babies curled up into 'toad like' forms, and started going to sleep. They all did it at once. 
Something else that was odd to me was that when you pick gerbils up, even if very friendly, they're always super active. They never really sit still. And they never let you pet them, but this was different. Of course, I started freaking out and tried to rouse one, but when I picked her up, and she was completely limp. her eyes were slightly open, her breathing was normal, but absolutely no movement other than respiratory. All the others were like this too.
I didn't want to make anything worse if maybe they were in some kind of shock, so I let them be, and watched them very intensely for about five minutes. At the exact same time, they all got up and started acting perfectly normal. 
Later, I added a tunnel to the male side of the tank, but by the time I had finished putting it in (about two or three minutes) one of the males went back into that state. A minute later, exactly like last time, he was perfectly normal. 

I've never seen a gerbil do this, and am happy to see they're all okay. I've been checking on them a lot and making sure everyone's fine. I was very, very gentle and cautious when doing this, and not only that, but I've done this with pups of the same age before, and I've rearranged this litter's tank before. I was wondering if this was a sort of play dead instinct when they got stressed, or something like that.

Anyway, before I started wondering if I need a priest in my house, I decided asking The Forum was the best course of action, so here I am

[LilyandDaisy]

I haven't heard of a play dead instinct in gerbils, but I suppose it might be possible. A learned behaviour is possible, but then I would have expected to see the parents behave like this in order for the pups to pick it up.

Gerbil pups of about 6-12 weeks of age can be prone to seizures which tend to be triggered by new environments or changes to their environment, and which can look like playing dead or going limp. If this happened to just one pup I would assume a seizure, although I think it is unusual that it happened to every single pup in unison. Seizures are considered to be genetic, so perhaps the whole litter is exceptionally prone to seizures? You could try handling them outside their enclosure, including in a different room to the one where their enclosure is, over the next few days and see if they react in a similar way. Seizures tend to start at about 5 or 6 weeks of age which might explain why they never reacted like this before.

[Shooting Star]

Pups don't have a "play dead" instinct, per se, but they do have a "freeze" instinct-- which when exaggerated, becomes freeze seizures. Involuntary stillness when stressed is helpful to avoid being spotted by predators, but when freed from the pressures of natural selection, it evolves into prolonged unresponsiveness and even convulsive seizures. As I understand it, that's why gerbils have a baseline tendency towards seizures unless bred with special attention to eliminating it-- because all of that is tied to the original "involuntary freeze" that is helpful in the wild.

[TJ's Rodent Ranch]

Okay thank you!
I haven't been on the forum for a little while now, so sorry I didn't get back to this sooner.

It seems like seizures definitely might be a concern here... would you recommend I keep the stress of these pups as minimal as possible, such as moving them before altering the tank, handling gently, etc.
WD40 and Frank have always given me very healthy, happy, and friendly pups, as well as unique and interesting colors, so I'm hoping they can continue to be a mated pair- however, first priority, I don't want to endanger any pups. If their pups have a genetic tendency to seizures, would you recommend that I not breed these two? I hope I got that right...

Also, is there anything you recommend I do for this specific litter, and is it okay to sell these pups?

I didn't think that this might be a problem, so thank you for letting me know!