The sound of thunder after dosing off.

Recently I had been meditating, cultivating the energy flow in the body. I laid in bed and unbeknownst to me at the time, I was asleep. I thought I was awake. I laid in bed and I was thinking that the pillow, bed, and room were like my cradle, an energy I was at home with. The same kind of thought that makes every place you go to feel like home.
The exact moment I had that thought, about being at home cradled as and in energy, I heard a monstrous sound like thunder. Exactly like thunder. It scared me and I started thinking that is energy too, it must be normal, no need to fear. AFter that I heard it again, and then I vibration all through my body.
At that point I was too alarmed and I jolted to find that I had been asleep the whole time.
Anyone have experiences like that? Of sounds?