G'day,

Experiences like this are exceptionally high powered. High energy OBE will produce/encounter some peculiar phenomena, including the deep humming, which will deepen according to your state of being. And at times, a light structure can be produced in this type of OBE. I think that part relates to the Merkaba light ship coming into being, if only partially.

I have no idea why you were on your back.

If you focus on that sound, remembering and 'tuning' into it, it can help bring on the OBE exit.

robert