I prefer comparing it to being in a fog because in a tunnel you would be surrounded by darkness but it isn't really like that. It's more like everything is hazy and blurry and indistinct. When you first go into the fog, the fog isn't real thick but the longer you're in it the deeper the fog becomes. Even then, occasionally the fog will lift a little and a little clarity will make it through but then the fog settles in again. Eventually the fog starts to lift and things start to become more and more clear.
The tunnel analogy sort of works for describing the beginning and the end but otherwise I don't get it. Dd you ever drive through a thick fog? It's much more like that. Just my opinion.