Shellshock

Shellshock is a state of reduced reaction time, slowed movement and firing speed, blurred vision, and muffled hearing due to a nearby explosion. While shellshocked, a faint ringing noise can be heard. As the shellshocked state ends, a whistle can be heard, reminiscent of Saving Private Ryan's interpretation of shellshock. The title is based on the medical condition shellshock, caused by traumatic experiences in warfare.

Appearances
Shellshock appears in Call of Duty and Call of Duty 2 when the player is nearly hit by artillery, and lasts anywhere from five to ten seconds. In Call of Duty 4: Modern Warfare, and Call of Duty: World at War shellshock occurs in singleplayer when a nearby explosion detonates. In Call of Duty: Modern Warfare 2, shellshock occurs when a Stealth Bomber flies overhead without killing the player, and in Call of Duty: Black Ops, a B-52 or Mortar Team. It will last anywhere from one to ten seconds depending on how close the player is to the explosions.

Call of Duty and United Offensive
In Call of Duty, shellshock only occurs in campaign from mortar blasts, tank blasts, and grenade explosions. However, it does not occur in multiplayer. United Offensive changed this by adding shellshock to multiplayer from all explosions. The length of the shellshock depends on the amount of damage taken from the explosion, not directly on the distance from the explosion. Explosive damage sustained in a vehicle results in shellshock 1 second long, no matter how much damage was done.

Call of Duty 2
In Call of Duty 2, shellshock occurs in both singleplayer and multiplayer. In the latter, it is mostly caused by grenade blasts.

Call of Duty: Modern Warfare 2
In Call of Duty: Modern Warfare 2, shellshock occurs in the campaign towards the end of loose ends and from Precision Airstrikes and Stealth Bombers attacking an area close to the player. If the airstrike does not injure the player, shellshock will occur, resulting in effects similar to a stun grenade for a short period of time. It is most likely to occur during a Stealth Bomber carpet bombing run.

Call of Duty: Black Ops
In Call of Duty: Black Ops, shellshock occurs when the player is near falling mortars or near the bombs from the Rolling Thunder. Most of the time when the player is near the Rolling Thunder bombing, they will sustain some damage, if not get killed.