What you're describing sounds like what some people experience in times of great stress or anxiety. They often say that it was as if they were watching themselves from the corner of the ceiling, looking down upon themselves, just a general 'out of body', unreal sensation, as if life were a movie, and so on. I often feel this way when walking to school and I get absorbed in my own thoughts. I think the sensation is more likely to happen if you're listening to music, and you're quite prone to day dreaming.