I did it for about a week. That's how long I was in Miami with my parents, eating good (tasting) Cuban food. Though I watched my ratios a bit, of course I partook of the usual high-carb Cuban meals and desserts.
And felt like shit. Good thing I didn't have to do anything at any particular times. Went back to needing 1-1.5 hours more sleep every night, and feeling sluggish. The sleepiness at 3 and 9pm came back. The "drunk" feeling after over-indulging in carbs came back. I used to attribute this to tiredness, but now that I'm paying attention I see it's completely different. It's a mental thing, as if I had been drinking, not really a tired feeling. I'd be better off driving drunk than in that state.
I think I'm mostly back to normal now, took over a week.