What is the nervous system designed to do? Nerves make the arms and legs move. Nerves make the heart beat and the lungs breathe. Ultimately, the entire nervous system is designed to keep the body alive. That is its most primal function. If a lion is chasing, the body runs. If the hand touches something hot, it jerks away. Just like a built-in alarm system, this system of nerves will alert the body to danger and trigger automatic protective responses. Normally, this system works beautifully and life is preserved well into adulthood.
However, in some cases, this alarm system goes haywire. For example, some people are born with the inability to feel pain, a condition called the congenital insensitivity to pain. That condition is not a blessing, but a curse that leads to insurmountable body damage and a premature death. The nervous system can go haywire in other ways too. What happens if this alarm system is too sensitive? Now instead of feeling no pain, one is left to feel too much pain. Just like a car alarm system that triggers anytime the wind blows, an overly sensitive nervous system can lead to false alarms and alarms that never turn off. Scientists have studied the process that leads to an overly sensitive nervous system and have called it nervous system sensitization.
The sensitization process is usually triggered by something that is perceived as a threat. The trigger can be an accident, an emotional response, an immune response or any number of events. The exact who, what, where, and when remain a mystery. After the triggering event, the input "threat" signal is received and an output is generated from the peripheral and/or central nervous system. In many cases, the output signal is pain. Depending on the intensity of the input "threat" signal, the nervous system will stimulate, also called "wind-up", other signal receivers and output messengers in order to increase the system's capacity and capability to sound the alarm and handle the threat. Normally, this "wind-up" sensitization process is self-regulating. But sometimes the system goes haywire and the nervous system remains sensitive long after the threat has passed.
In this sensitized state, the peripheral and/or central nervous system will have many false alarms that are triggered by normally non-threatening activities like walking, sitting, standing, talking, breathing, and moving. These false alarms cause life for someone with a sensitized nervous system to be a hellish state of constant pain and agony over seemingly benign activities. Flare-ups that happen with no rhyme or reason lead to a life of fear and anxiety. Afraid to move, a person can become trapped inside her/his own body that is full of sensitized nerves.
In this sensitized state, sometimes the alarm does not turn off. More annoying than a car alarm that will not shut off, more annoying than a fire alarm that will not shut off; the sensitized nervous system is in a constant state of threat. Hence, this faulty alarm system can generate a constant signal output of nerve pain, even when the threatening "lion" is gone.