With respect to this idea, I'm not particularly interested in either of those goals. More the general longevity and health improvements that come with regular exercise irrespective of weight loss or muscle gain [1].

I haven't been able to find much in the way of research on the tolerability of EMS during sleep. I would be surprised if the idea is actually feasible. It just seems like it would be such a big win if it was.

Personally, I frequently toss and turn and breath heavily, and wake up with a high heart rate. But then, my sleep quality is terrible and when I got a sleep study the sleep phase diagram looked like a seismograph reading during a 4 hour long earthquake, so...

1: https://theconversation.com/exercise-extends-life-even-witho... (Maybe not a great source but I think there is a wealth of evidence for this)