Mihaly Csikszentmihalyi's talk at ted starts very slowy and it takes about 8 minutes, till he finally cuts to the chase.
He describes the emotional state that many people experience when they are completely immersed in a challenging task they like.
The flow is something that I sometimes reach when writing software, plan or design something I care about. A ringing telephone then feels like an alarm clock waking me from a dream state. It seems to come from a completely different world.
It's funny, that he mentions people reaching that state when watching television. I remember, that it happened to me, when I was a kid.
His explanation is interesting. The mind has a limited capacity. You can only do so much at one time. When you are totally immersed in some creative or challenging task, there simply is not enough processing power for self awareness.