Stress
Stress is used as a catch-all term to describe all stressors affecting a character, be they mental or physical.
Characters can accrue stress by being tired, starving, dehydrated, or overfatigued. Harrowing or traumatic events as well as environmental factors can increase stress, such as hypothermia, exposure, sunburn, or heatstroke.
Higher levels of stress lead to greater penalties on rolls, and additional detrimental effects, such as wounds or HP damage.
You can track your current stress with a d6.
Stress heals differently depending on the source of the stress—for instance, stress from lack of sleep can be alleviated by a good night's rest. Stress from hypothermia will start to fade once you get warm by the fireside.