Unconsciousness is the result of an injury or multiple injuries in a small span of time causing a player's Shock stat to drop below 25 in DayZ. While unconscious, a player will be unable to open their inventory or see their status, and their screen will be black. All audio is heavily muffled, and the player will "fade" in and out of consciousness, where the black will clear up slightly before blacking out again. Players will not come to consciousness until their Shock stat recovers back up to 50 with them recovering 1 Shock/per second while unconscious leaving them like that from anywhere between 26 to 50 seconds depending on where there shock is when they fell unconscious given nothing else causes further shock.
The player will be unable to move or interact with anything, leaving them in a vulnerable state where others can loot, tie the player up or even kill them without resistance. The player will eventually wake up from unconsciousness unless they have bled out too much (<3000 blood), at which point another player needs to stabilize and heal the unconscious player, and either leave them to recover on their own or use a IV Saline Bag or a compatible blood type IV Blood Bag on them to restore their blood more quickly.
Then you can do CPR to improve the speed at which Shock is recovered by an additional 2.5 Shock/per second for a total of 3.5 Shock/per second cutting down the time they come to consciousness to less then a 1/3rd of what it would be, or you use an Epinephrine Auto-Injector to immediately wake them up. However they will fall unconscious again rather quickly if they are below 3000 blood when the Epinephrine Auto-Injector was used. And CPR will remain ineffective until there blood recovers up to this point as a player sustains 20 Shock damage/per second when below 3000 blood.
You will also die if you try to log out while in the black screen.