It seems to me that life and death are not opposed to each other in a binary way but on a gradual scale, so that we can be more or less alive and more or less dead. Sleep seems to be a “little death” and therefore, on the other hand, death might be nothing more than “big sleep”.
Most people assume that we are either alive or dead. I, however, think that we will gain better insights into the nature of life and consciousness if we adopt a non-binary view of the matter.
In my view life and death are relative phenomena on a scale similar to day and night where we have all kinds of intermediate stages.
So that’s my framework for saying that sleep looks like death to some extent, and that death is only more of what sleep is to a lesser extent.
During daytime we are very much alive; that’s aware and in motion. But during sleep we are (almost) calm, silent and motionless, and we have (almost) no experience at the physical level.
Even more so this is the case in a comatose state of mind where we are totally unconscious. However, neither sleep nor coma is as much of unmoving and unconsciousness as is death and therefore death is further down that scale.
Sleep and death in plant life
If we look at plant life, I think this point is even easier to observe and realize. For example, flowers open up during the day and shut down at night, so it looks a lot like if they are awake during the day and sleeping at night.
But in winter plants have a more radical sleep that is “dead-like” to a further degree.
So, for example, the flowers, fruits and leaves of trees disappear in winter. These parts of the trees fall off and thus become dead flowers, fruits and leaves.
The trees themselves also look as if they were dead, but of course they are not completely dead and in spring they “come back to life” again.
So when it comes to plant life, it is relatively easy to see that the sleepers and the dead have some similarities.
To say that sleep and death are consequently the same is too much, but I think the two can best be understood as different phenomena on the same life and death spectrum rather than completely separate and diverse phenomena.
No real death?
Going a bit further down this line of thought it seems to me that the life/death scale is really a presence/absence scale.
Apparently life is the “presence” of consciousness, whereas death means “absence” of consciousness (on the physical level).
Where consciousness goes during its absence, we cannot know for sure, but when we are asleep it is supposedly in “dreamland”.
If it is true that sleep is actually a “little death” then, on the other hand, death might be just a “big sleep” where we have departed from the physical plane to go somewhere else but where that absence of consciousness is not necessarily tantamount to its extinction.
Personally, I think the scale indicates that there is no real death but only the coming and going of life and consciousness on the physical level.