Emotional intelligence refers to the capacity for recognizing our own feelings and those of others for motivating ourselves and for managing emotions well in ourselves and in our relationships - Daniel Goleman 1998 Working with Emotional Intelligence.
This is from a blogpost I found while researching the issue.
EMOTIONAL HIJACKING: THE TRIGGER TO AN UNHEALTHY MIND
Posted by Saif
Emotional hijacking is a state when an individual's cognitions are overpowered by his/her emotions. It is usually referred to in the context of aggression or fearfulness.
With respect to aggression, it can be said to be a sudden unleashing of rage towards another person. It is an extreme emotional outburst or an emotional explosion caused by an incident that may trigger anger or fear in an individual.
Such incidents happen many a times. There are a number of situations in which a person might get angry or upset and without even thinking about anything he/she might just lose his/her cool and simply explode with emotions and attack the other person verbally or even physically. For instance, an individual might suddenly get extremely angry and begin to shout at his/her friend and even slur him/her. In an extreme case, a disgusted husband might suddenly get upset and beat up his wife badly. In more extreme cases, a person might kill another person with an outburst of anger.
Wife beating and killing a person due to emotional hijacking can be rare, but incidents of individuals quarreling with each other and in the process damaging a relationship are quite common. Such moments do not last very long, but the time that it lasts does enough damage. Most of the times, a person regrets getting into such an act.
Research shows that such emotional explosions are neuralhijackings. In such a moment, a center in the limbic system (a part of the brain), the amygadala, the seat of all emotions in the brain, takes over the neocortex. The neocortex is the part of the brain that is 
responsible for our thinking. During thismoment the neocortex stops functioning. The amygdala gets triggered and in an instant takes control of the brain, in a sense hijacking it. Thus, it is called emotional hijacking.Emotional hijacking does not occur just like that out of no where. Usually certain past events that are disturbing to the individual keep building up resulting in the sudden emotional outburst. If a person is facing some problems for quite some time, they start playing on the mind and a moment may occur when he/she cannot take it any longer, which may result in the extreme explosion of emotions. A person may be too stressed out, or a person might be a bit angry for something that might have occurred before. In such a moment if something happens that further causes distress, then the chances of emotional hijacking to occur increase to a great extent.
Emotional hijacking takes place in an instant and by the time it gets over it can do a lot of damage to the person in many ways. If emotional hijacking keeps on occurring time and again then, it will have an immediate negative affect on the individual’s ability to have relationships as well as the quality of his/her current relationships. Emotional hijacking occurring too often in a person will give the impression to others of the individual being a loose cannon. People will begin to dislike his/her behaviour and may keep a distance from him/her. Likewise, his/her peers, friends, and others who are close to him/her may begin to dislike him/her, because nobody would like to be at the receiving end of a person’s extreme rage, especially when the person has a close relationship with them.
Emotional hijacking also creates a lot of negativity within the atmosphere. If a person due to an extreme outburst of anger shouts very loudly it has a bad affect on the mood of not only others, but also on the individual himself/herself. Such an emotional outburst is not at all good for the mental and emotional stability of the person. One incident of emotional hijacking can lead to a severe mood swing, so one can imagine what will happen if this happens very often. Such kind of behaviour will also increase the stress level of the person. In extreme cases it can cause high blood pressure and even heart problems. Therefore, emotional hijacking can have a very bad affect on a person’s mental as well as physical health.
Instead of facing the negative consequences of emotional hijacking it is much better to try to prevent it as much as possible. One way to do this is to try to reason and thus challenge the anger provoking thoughts. Emotional hijacking is more of an impulse driven reaction. The person should try to think before he/she reacts in such an aggressive manner and in a way try to hold back that impulse. He/she should try to channelize his/her thoughts to a more rationalistic way and try to bring down the level of anger. This is a very good way to counter emotional hijacking, but it is easier said than done. During an episode of emotional hijacking, a person becomes cognitively incapacitated. He/she almost loses the ability to think at that moment.
The best way to prevent emotional hijacking is to just move away from that place and go for a walk as soon as one realizes that matters can become worse. This works as a distraction from the anger provoking thoughts for the person. The person buys out some time, which helps in relaxation
of thoughts and makes the individual calm down. In such a situation the left prefrontal lobe (the front-left side of the brain) of the person comes into being. When the anger provoking thoughts get distracted, the left prefrontal lobe, which is responsible for maintaining emotional balance, works as a counter mechanism towards the amygdala and dampens its affect on the brain. Thus, the person comes back to his/her normal and calm phase and is able to prevent emotional hijacking.In situations like this, watching television or listening to music can also help in distracting one from anger provoking thoughts and thus make the individual calm down. Distraction from such thoughts also helps the person to get into a more pleasant mood. If a person goes out for a walk, he/she might find the surroundings pleasant, which will have a positive affect on the mood and make him/her happier at that moment. The same thing happens when a person begins to watch television or listens to music at that moment.
Other ways of preventing emotional hijacking is deep breathing and muscle relaxation. This helps in changing the body’s high arousal of anger to a low-arousal state. It also, in a way, works as a distraction from whatever triggered the anger.
It is very obvious that emotional hijacking is a very unpleasant phenomenon.The consequences of emotional hijacking are nothing but bad, be it on mood, relationships, or the overall health of the individual. A person should always try to be in a positive frame of mind and try to be as emotionally relaxed and calm as possible. The more positive frame of mind the person is in the more chances are that he/she will be away from emotional hijacking and the more chances are that he/she will be an emotionally healthy person.