Emotional Flooding happens when one or both partners pulse rises quickly casting emotion to be stronger that reason. When you are neurologically emotionally flooded you say and do things in an extreme fashion that are often damaging to the relationship. Julie Gottman interview explains how you have to take a break at least 20 minutes and not talk about the fight. When both are calm, and it can take more than 20 minutes but that is a minimum, you can try again.
Stonewalling is when a person is actually emotionally overwhelmed and instead of expressing the overwhelm actively with outward intensity, the person detaches and appears to be cold to their partner and uninterested in what they are saying. Stonewalling is actually for form of flooding and a signal that that person needs to take a time out of at least 20 minutes or more, until they feel safe and can actually engage with the other person.