When somebody invents a way to hit the Maximum Productivity Zone at a time other than 2:30AM, let me know. Mountain Dew is a catalyst --- but I need this mindset at 10:00AM, not when I'm burning the midnight oil.
Sit down, without the television - without the radio. Drink your coffee (whatever).
Read. Read your own code. Read it from top down, function by function. Look for places that need better comments. Read programming stuff. Do internet lookups for all of the stuff you are currently working on.
Do not post, do not read quips about vacations, do not search for that new $stuff that you don't have, and do not post. Did I mention... don't post?
At some point during this excersise - you'll get an idea, and start thinking about it.
This should naturally transition into "the zone". Otherwise, it will transition to "back to bed", but maybe that's just me.