Hi.
Look what happened to me and others:
I went in a noisy car on a long trip and I was very tired. So I laid down on some chairs and tried to sleep. After few minutes suddenly I realised that the noise fades out very fast. Like my hearing sense was shut down. When I realised this, it shocked me a bit and the noise came back (from the car). I asked many persons and they told me that this happened to them.
This means that I started to fall a sleep while being conscious? I mean that I was aware of my own sleep onset?

Paul