I don't get tunnel vision, but I think I definitely get "frame vision".
You get sucked into what you are looking at, like a film or computer screen, and are able to ignore everything around it.
Kicking that habit (or at least knowing it's going on) can really help with drawing, because you pay respects to the subject's orientation and your canvas' orientation.
Anyway BIG LIIIPS. I kept moving my head so I got the perspective all nuts.