Your health and stamina should be regularly checked. If your health depletes to 0%, you will die. Your health is the red body indication. When your health reaches your feet, you will no longer be able to sprint, and your screen will turn black and white.
Stamina is the orange circle around your health, hunger and thirst. Stamina allows you to sprint, and it depletes rather fast compared to how it recovers. When your stamina bar hits 0%, you will no longer be able to sprint.
Stamina can be recovered by waiting it out, and also by drinking or eating special items.
A few examples: water, energy drinks, granola bars, electro-aid.