When something disturbing happens, it gets stored in the brain in a way that our human system feels like that event is either going to happen again at any moment or is happening now. This is stored physically in the brain. When some event happens that may be similar or just has an element that reminds the system of that disturbing event, the brain reacts as if the original disturbing event is happening. EMDR helps to move the storage of that memory to a more functional part of the brain that can experience the event as actually being in the past. It is important to know that there is a real physical change happening with EMDR. The events that previously activated the brain into over-reaction no longer have that effect. The person can now react to the present without the past interfering.
Video: https://youtu.be/HNdMHuwvF_M
EMDR does not recover repressed memories.
The brain is doing only what it is able to and feels comfortable doing. EMDR only assists the brain in reprocessing unstable processed memories. If the brain has locked away a memory, it has done so for a reason. This therapy will not unlock something that your system is not ready for.
Article: https://emdrhealing.com/emdr-repressed-memories/