In real life you can feel exactly how tired you are and you can also quickly assess the severity of a wound, but in a game this is impossible without some sort of metaphorical hint.
It would be useful to have a simple visual gauge showing the percentage of your fatigue & health (like in wasteland)
It would also help people understand the new fatigue system much better if they can actually see it working in front of their eyes :-)
Obviously make this optional in the settings so the hard core players can turn it off :-)