It sounds like you were in a non-physical focus (or a dream). But you started to get aware of your physical body instead and therefore got out.
But I hope you reality checked after this... Sometimes you can still be in the dream.

And also remember how your awareness or how you felt when you were in this state, it will make it easier to catch false awakenings.
Next time don't open your eyes an keep laying still and the rest should take care of itself, no matter what stage you are in.

Good luck!