Are you sure that guy who wakes up tomorrow after you've gone to sleep is you?
Or the one who wakes up after 10,000 sleeps?
I'm sure he's going to be quite different...
Maybe that dude (the one who woke up after you went to sleep) is another you, but slightly different. And you, you're just gone.
I cannot be 100% certain that sleep is not fatal. If I had some safe and reliable means of preventing sleep I would take it without hesitation. But it seems plausible that a person could survive sleep because it's a gradual process and one that everybody has a lot of practice doing. However, there are no such mitigating factors with general anesthetics. I will refuse general anesthetics if I am ever in a situation to do so. I believe a combination of muscle relaxants and opioids can serve the same medical purpose, which I do not believe would kill the person.