OK. Again, we're not talking about killing an infant. We're talking about aborting a fetus, there's a difference there.
The distinction I'm getting at is that someone who was sapient, sentient and self aware and then went to sleep and temporarily suspended those faculties, to resume them upon waking up, if you kill them, you've interrupted the life of someone who had developed an identity, personality, thoughts, likes and dislikes, and relationships, both to the world around them and to other people, what we may call in short "personhood" and if you kill them, awake or asleep you've interrupted that. Now it may have been on a brief hiatus while the person was asleep, but those processes resume from where they left off as soon as the person wakes up again.
If you abort a fetus which would have none of those things, you're not disrupting anything but basic biological processes, like cellular metabolism and division. But the point is, all those things that really define the experiences of a sapient, sentient and self aware being don't exist yet, and have never existed. The potential to have "personhood" is not the same thing as being temporarily unable to act out "personhood" because you're asleep.
The distinction is this. Let's say you're a student and you're working on a large paper. You save the document, having written half of it, and then the next day you come back to it, but the file has accidentally been deleted and you have to start again. Now, while you were away and the document was saved on your computer, the document was not a living work. It was simply something you'd written that was waiting for it to be modified, it would become a living work again once you sat down and attempted to come to grips with the issues you're discussing in it, but until you did that, all it's livingness was completely suspended.
Alternately, let's pretend now that you've just opened up a fresh document to start writing your paper, you sit down, and then close the document and decide to go eat a sandwhich instead. You'll start later.
Now, if we extend your argument to my document metaphor, these two things are exactly the same. Deleting a half completed essay, and closing a blank document. I suppose the distinction is that in the case of killing a sleeping man, you've ended something that already existed.
In the former case you're just removing potential for something which doesn't exist yet, to exist in the future.