There are a great many sayings that make little sense to me. One of the silliest is "you can sleep when you're dead." I get the sleep/death analogy, but really? Can you sleep when you're dead? I'm pretty sure that, when you're dead, you stop sleeping. It's not really 'eternal rest,' so much as, you know, death. I mean, maybe it's restful, I don't know. But there's not really any evidence that suggests death is like sleep.
Personally, I like to sleep. Not only do I function poorly when I don't get my 8-9 hours, I also enjoy laying around in the morning, waiting to get up. I like dreaming. I like the 30 minutes while I'm falling asleep when I think about some complex question and let it drift into the increasingly nonsensical stuff of dreams. I like waking up in the middle of the night, seeing that it's only 2 AM, and going back to sleep.
And, as far as I know, I can't do any of that when I'm dead. So, no, I can't sleep when I'm dead. And neither can you. You can sleep only when you're alive, so I advise that you do so, lest you miss out.