When I was a kid I loved playing Chrono Trigger and in the ruined future of 2300 they had a device that could give you a full nights worth of sleep in a few seconds, but it didn't alleviate the looming starvation.

As far as I'm aware, sleep has two gundementally unrelated functions: body/immune system repair and memory processing. The reason we need to sleep every day is more of the memory processing and that's the stuff that will kill us after a couple of weeks. But the other function is almost certainly as important even if it doesn't technically need to be done as often.

So, if you could design a machine where sleep was entirely REM sleep, in theory you could get all the brain rest in under an hour.

Does anyone have an idea of how long you could then go doing this every night before you needed the more psychical repair done? I guess that would depend on if the machine that causes the constant REM can make sure the hormones are properly regulated, and in this scenario, let's assume that's the case.

I was thinking maybe that you'd probably want to cycle in a few days of normal sleep somewhere between twice a month and once every two months, but I'm more pulling that out of my ass than anything else. One of the big problems is how much of the physiological strain of sleep deprivation a direct cause of not being able to do the body maintenance and how much is the stress of your brain being strung out? I'm not sure anyone has so much of a model on how we could parse this out, but that's why I'm asking here.