We talked a bit about this on one of the other threads. I wasn't sleeping well at the start of my IF experiment but find that I'm sleeping well now, eight days in.
I'm no doctor, nor do I even know enough about the body to be a layman, but I'd say when you throw a major upheaval at the body like an IF, it takes a little while to adjust. Eight days in and this seems like a breeze; the first days sucked ass.
and my wife thinks this is completely rational, which scares me slightly.