A B777 Captain reported experiencing extreme fatigue on an unaugmented international flight.

Narrative

The level of fatigue on this flight cannot be overstated. I am deeply concerned with the condition of myself and my First Officer on this flight with regard to fatigue and sleep deprivation. This is only the second transpacific international flight in five years that I have flown that is unaugmented; this after multiple sleep disruptions; flying on the backside of our body clocks with consecutive circadian rhythm disruptions. We were both exhausted from the flight planning phase to the landing. It is of great concern that we are scheduled to fly these trips with no consideration to the cumulative effect of sleep loss. The only consideration is that this one flight is under 8 hours block to block as if we are coming from days off; fully rested. Its 7:48 block to block and an accident waiting to happen in my opinion. When both pilots unintentionally fall asleep at their stations; safety is seriously compromised. Clearly; this flight should be augmented. We have the ability to measure fatigue by cumulative sleep loss and circadian disruptions and this information should be used to consider the need to augment.