We are led to believe that he wakes from the coma in 2007, but, at a meeting, somebody draws his attention to the fact that he has been idly cutting his finger with a piece of metal without realising it. He remembers what the barman in the 70s said - if there's no feeling, it's not real - so he knows that 2007 is an illusion. He jumps off the building to end the illusion and 'wakes up' back in the 70s. What is really hard to explain is how he knew so much about the future - mobile phones etc. Well, that's what I think.