Have you tried it?
To be so engulfed in something that you forget time and space, and only focus on what you are doing at that exact moment in time?
Flow, as used in psychology, was named so by Mihaly Csikszentmihalyi (try say that fast three times!), and he studied when people were most productive, and created their most compelling work; when they lost themselves in what they were doing. Watch him give a TED talk on the subject here.
It happened to me the other day. I was drawing and listening to classical music, and all of a sudden 1½ hrs had gone by and I hadn't even noticed. It was wonderful! My brain was switched off from all distractions, and the only things that existed were my pencils, my hands, the paper and the image in my head I was drawing. I can't say it was the best piece of work I have ever made, but the feeling afterwards was fantastic. It felt as if I had slept undisturbed a whole night (I have a young child, so that doesn't happen often), or been injected with some magical energy drug. I had a great sense of accomplishment and a positive vibe that stayed with me for a long time. I was happy.
Flow happens to me when I am creating something. A drawing, a photograph, whatever. When I am using my hands and my brain to translate something from an idea to an actual object. When I am feeling challenged and in control at the same time. I am hunting for that feeling now, every day I try to find it, and I am enjoying the chase.
Have you found your flow?