Extreme Emotional Disturbance (EED) is a New York-specific defense in Murder cases only. To be clear if you are found to have committed a murder under an EED, you would be found not guilty of Murder, but guilty of Manslaughter.
EED is a very different defense than claiming insanity or mental disease or defect. First, you must have suffered from such an extreme emotional disturbance, that you suffered a profound loss of self-control. Whatever the emotion, whether its sadness, anger, fear, or any other, it must be very intense. Second, there must be a reasonable explanation that you suffered this extreme emotion. The reasonableness is viewed from your own viewpoint and situation, not that of another person. Finally, you must commit the murder while under the influence of that extreme emotion.
Often, this defense is compared with the example of walking in on your partner in bed with another person and acting immediately. In such a circumstance, even if a police officer were standing right next to you, you very well would have acted the same way. Like mental disease or defect, while an expert witness is not mandatory it is often necessary to support this defense.
If you were in a minor car accident and were so angry that you went and purposefully killed the other driver, you may very well have suffered from an extreme emotion, but most jurors would be unlikely to say such extreme emotion was reasonable because of an accident.
If you planned some or all the murder it is less likely you acted under the influence of an extreme emotion. Also, if there was a time frame when you “cooled off” it is possible that the emotion lessened or ended and you instead made the conscious, intentional choice to act as you did.