1st time was IMC in the back of a 172, watching another student. I guess that's the best place to get it, trusting the PF does not get it either.

Another time was (again, IMC) being vectored for an approach. During the turn, the sun bore through and confused the brain.

All your can do is ignore it and concentrate (concentrate, Manny Mota) on your scan.

The more you fly in the soup (or hood), it should happen less and less.