Unconsciousness
You can become unconscious in game as result of low food/water/blood, getting hit by a zombie too hard, shot, an infection or even a bad crash. When you become unconscious your screen will turn gray and a sand clock will be displayed in the middle. You will not be able to do anything while you wait for the sand clock to run out as you are unconscious. When you return to your conciseness you will usually be bleeding and low on blood, at that point the best thing you can do is find a safe place such as your house where you can begin patching yourself up and getting back to health.
Luckily if you are unconscious your friends can help you by injecting you with Epinephrine
, also known as 'adrenaline' which will get you conscious again quickly so you can patch yourself up before you fall unconscious again.
To inject someone with Epinephrine a.k.a an 'Epi Pen' approach their body and select 'Give Epinephrine' in your action menu.