Incapacitation is the state of the player, when they have lost all their health.
If the player loses all their health, they are incapacitated. In this state, they cannot move and have their view locked in the direction they looked, when they were incapacitated. On any other Game Mode than Hard, the player may Respawn with certain degrees of penalty. On Hard, the player must be picked up and carried by someone else to a Simple Bed or Hammock, or reload the game from a previous save point.
Being revived in a bed gives the player back a certain amount of health and stats: see the above-mentioned Respawn page for more information.