Studies of people in deep slow wave sleep show that they were experiencing a desultory kind of ruminative thought when woken. It’s hard to catch and not remembered. But as you say, neurons never stop firing. So the brain can only be turned down low, not shut down.

Good point. The fact that we don't remember experience doesn't mean that it wasn't there.

So we should be cautious what we assume.

Anyway, hypothetically, suppose that there really isn't any experience during deep sleep, just as there isn't after complete shutdown at death

Well, just before that complete shutdown and absence of awareness (in deep-sleep or afterdeath-shutdown. ), you, by definition, have awareness. But most likely, when you're that nearly shut-down, you don't know about waking-life. Or identity, events, time. ...that there are or ever were such things. ...or that there even could be such things. At that point, you've reached timelessness.

Sure, shutdown occurs soon, but you don't know that, because you've reached timelessness. So the temporariness of your experience just before that shutdown is meaningless.

But, as you pointed out no one can say that there isn't any experience during deep sleep, just because we don't remember it.

There are things that your survival requires you to know. What it was like in deep sleep isn't one if them, so it isn't surprising that the body doesn't provide you a memory of that time. Aside from that, most likely it's so close to what the "awake" person would call "nothing" that there usually doesn't seem to be anything to remember. Maybe there isn't any of what waking consciousness would call something. But, from your point of view when you were in deep sleep?

Of course, after death, when the body and awareness have completely shut down, there's no experience. So you'll never experience a time without experience. Only your survivors will experience the time after your complete death-shutdown.

Michael Ossipoff

If you ever had general anesthesia you'd have personal experience that sleep is a much higher state of consciousness than anesthesia. When you're asleep you are aware of sounds and will wake up if you hear something unfamiliar. Dreaming can be just as realistic as being awake. But when you're in surgery you are gone. You do not exist. They turn you off then they turn you back on. Sleep is closer to waking than it is to anesthesia.

NYT wrote about this a while back. http://www.nytimes.com/2013/12/15/magazine/what-anesthesia-can-teach-us-about-consciousness.html