not to impose but your question concerns me a little.... take a piece of criss crossed draft paper and look at it closely. If the lines look like a fishnet under water go to an opthamologist right away. That was what I did and it turned out to be retinal problems. You never know
I can't be sure and am purely speculating, but suspect that your focusing muscles may have beein going through some spasms or difficulty relaxing or perhaps when you lied on your back you developed some horizontal nystagmus type eye movements that lasted a bit. Overall, I'm really not sure. If it happens again, tell your ophthalmologist about it and have a check up.
Michael Kutryb, MD