In my extremely basic way of explaining as I’m no expert, brains have a left side and a right side.
Every day, the brain receives information in the left (I think) side - conversations, sounds, smells, the way you jumped when a car horn went off etc.
At night the brain filters this info and chucks out trivial stuff and processes info into the right side, where things are stored like little jigsaw pieces of memory.
In the case of big trauma, the right side of the brain sort of goes ‘That’s awful info, I’m not accepting that!” therefore the info isn’t processed.
Unprocessed info then stays in the left - here and now - side, so it continues to feel like it’s happening now.
The consequence of this is that you feel the same sense of danger/fear etc you would have at the time of the trauma.
EMDR is a method whereby this trauma is processed into the right hand side. Here it becomes a memory. You don’t forget it, but you no longer feel the emotion about it (or as much)
It involves talking about the trauma whilst either tapping your shoulders or following the therapists fingers going left to right, with your eyes.
In my experience it works xx