I Was Thinking About Work This Morning, Nothing Bad, Just

I was thinking about work this morning, nothing bad, just putting things in order as a I lay awake, getting ready for the day and deciding what needed to be done first when something shocking happened to me that I have never ever experienced in my life and didn't think possible. My mind totally emptied and all I was aware of or could 'see' in my mind's eye was grey, a big slab of the colour grey and absolutely no thought or connection at all. I felt like my mind just dropped out. This lasted for about a split second, but I am still now thinking about the nothingness that I experienced. It was quite incredible. What happened to me?