Do you have a memory of a past event that disturbs you? One of the memories that used to disturb me a lot is when my dad passed away and I rushed him to the hospital in an ambulance. I would freeze every time I heard or saw an ambulance thereafter.
Here is a method that helped me come out of its grip. This may be of help to you too. I learnt this from Arul Dev.
1) Choose the memory you want to get freed from.
2) What associated image(s) do you see? What sound(s) do you hear?
3) Make the image smaller. Make it tiny. Move it to the distance, far away. If it has colors, you could try changing it to black and white. If there is an associated sound, reduce its volume.
4) Reject the memory – the image, the sound. Shift your focus to something positive.
You may need to be at this and repeat many times to see the effect.