EMDR therapy is a type of trauma-informed therapy used to treat trauma as well as other presenting concerns such as anxiety, grief, specific phobias, among others. Sometimes when a person goes through a lot, the harmful events get stuck in a part of the brain called the limbic system, which can cause the individual to get triggered by day to day stressors.
Let's say you used to be forced to take karate classes as a kid and remember feeling terrified by your teacher who would scream obscenities in your face. So, years later you find yourself in the frozen food aisle at a store, and a song comes on over the speakers that used to be on all the time during karate warmups. You find yourself feeling some type of way, maybe a heaviness comes over you or you feel a chill creep up your spine. You might get this overwhelming sense of "UGH! I hate this song!" All of these reactions are a good indication that some of that information has been stored in the limbic system, and is simply spilling over into your daily life.
What has happened is that, with traumatic memories, there tends to be a disconnect between the logical part of your brain that knows all of this is in the past (the neocortex) and the "gut level" part of your brain that has no concept of time (limbic system), which is all about flight or fight responses. You KNOW (neocortex) that your karate teacher is nowhere near you. You KNOW (neocortex) it was so long ago and that this "shouldn't" bother you anymore, but on a gut level (limbic system) it does. EMDR therapy helps these two parts of the brain communicate so you can come out with a more adaptive way of seeing what happened in the past… and not only believe these positive messages, but really be able to internalize them on a gut level.
So, here in our karate example, when you hear that song, the reaction that might pop up is "I'm in danger," and it makes sense because of everything you went through as a kid.
This trauma therapy process, however, helps you pull from other, more positive experiences and come out believing something like, "I'm free" or "I'm safe now" when you picture your karate teacher. If this is the case, then, imagine how different it'll be the next time that song comes on. The ultimate goal of EMDR therapy is to help move traumatic memories from the limbic system into your long-term memory so they don't affect your current relationships, goals, and daily life.