I went through a period of hypos last month and when I get below about 3.6 the light takes on a distinctly green cast, then the edges of my vision turns black - presumably the tunnel vision mentioned - and that progressively closes in and presumably would lead to me totally blacking out if not treated - it feels like I'm going at that point.
As a T2, has your BG come down drastically recently - because it might be a false hypo - when your BG drops a chunk, it takes a little while for your body to get used to the new lower levels and it goes into a sort of panic at higher levels than a true hypo. False hypos, in my experience and others have reported the same, give rise to more dramatic symptoms than an actual true hypo, which probably wouldn't happen at 4.2. I'd personally know I was getting low at that point, but wouldn't treat it as a hypo, I'd just eat something.
Edited to add: pop some more details about yourself in either your profile or your sig so that we know a bit more about you and can therefore help you better.