Incapacitated

You are on the brink of death.
You are unconscious, nearly unconscious, or alienated by the pain, so you cannot take any actions, the specifics are up to the GM.
Anyone next to you can instantly Execute you.
You can get incapacitated due to wounds, or due to fatigue.

Incapacitated due to wounds

In this case you must roll Vigor immediately, according to what's indicated in Injury. You could start Bleeding out, or worse, you could die.

If you manage to survive the incapacitated state due to wounds, each subsequent day gives the character an opportunity to roll Vigor and recover, according to what's told in the Healing section.

Incapacitated due to Fatigue

In these cases, the outcome depends on what is the source of the Fatigue. Check the Fatigue article.