Never having played the game, I can't really relate to that scenario... but I can most certainly imagine trying to stay awake while driving. Can't fall asleep while driving! I'm going to give this a try that way.
What other situations are common and familiar where we end up battling fatigue?
SKA what a brilliant idea!
Driving, or being in a meeting might not work as well because imagining it would be boring and battling fatigue would be very difficult. The soldier scenario is exiting, and this will make battling fatigue easier.
Also the
waiting element of this scenario is brilliant because it corresponds to waiting for the HI.
You can switch the enemies and the weapon to something that appeals to you, for example instead of defending against enemy soldiers with a machine gun you are defending against aliens with a laser blaster, or against vampires with a cross bow with a wooden stake, or werewolves with a revolver with silver bullets, Nazgul with Sting etc...
One point that can make a difference, it may be a good idea, while waiting on guard, to
expect the enemies, wish for them to come so that you can blast them. Because in theory if we associate the coming of the enemies with HI, then waiting expectantly for them to come may bring them sooner. But some sense of dread will be helpful too, because if we want them to come so we can blast without any suspense, then we may not be thrilled enough to stay awake.