Just One of the Future 500

Obviously 11 days was feasible. It's not really about longevity so much as the fact that the differential in sleep requirement due to damage and normal sleep keeps the damaged side dominant. However, I suspect with further experimentation it would be possible to keep going indefinitely, as the left hemisphere would simply shut down while consciousness switched to the right [...] Whatever sleep the right genuinely needs (and I do not know what this would be) could well be taken during "normal" left dominance.

Source: http://www.gelfmagazine.com/archives/staying_awake_by_switching_brain_hemispheres.php