The New Scientist has a article by Giai Vince (here) on research by Ilan Goldberg’s group on the lost of self awareness in some circumstances.
While people were being scanned with fMRI they were asked to make an identification of whether there was an animal on a card as it was shown. The test was done three times: slowly, quickly, and with an indication of emotional response to the card rather than the presence of an animal. The test was also done with musical clip identifying if there was a trumpet (slow and fast) and emotional reaction.
Goldberg found that when the sensory stimulus was shown slowly, and when a personal emotional response was required, the volunteers showed activity in the superfrontal gyrus - the brain region associated with self-awareness-related function.
But when the card flipping and musical sequences were rapid, there was no activity in the superfrontal gyrus, despite activity in the sensory cortex and related structures.
“The regions of the brain involved in introspection and sensory perception are completely segregated, although well connected,” says Goldberg, “and when the brain needs to divert all its resources to carry out a difficult task, the self-related cortex is inhibited.”
This seems, to my mind, a different cause for losing self-awareness then that which comes from very high levels of skill in a Zen-like activity or from some types of mediation. So we have at least three ways to lose self awareness: too busy for introspection, so skilled that thinking interferes with performance, having learned how to steer attention. Probably there are drugs that also eliminate self awareness.