I have found I do something similar, and my T explained how in the brain there is a certain pathway (Sorry I cannot give all the correct terms) that reacts to things that are threatening.
This pathway is a very quick one, as it has to be in order to give quick reactions so the person can react to save themselves from the threat of, say, the sabretooth cat they have just seen. Whatever you do will be a learned reaction, probably from childhood, and it is deeply ingrained.

If you have learned to block emotions, because they are too overwhelming and didn't help, then this blocking will happen in milliseconds, before you even notice them.

You can learn to change this thought process though. It does help to be aware of it. Think of it as gradually learning to deal with each step of the process.

I learned that I was diverting my thoughts to protect myself from things I could not deal with. First I had to learn that this was happening, then to acknowledge it, which actually took me months. Then I slowly learned to recognise when it was happening, but only noticing it a minute or two after it had happened. Then I stepped back each time to find what the particular threat was that I had reacted to. Now I am part way through learning new ways to react that are more effective.

My T told me that I should acknowledge the previous methods helped when I was little, but that now they are creating other problems, so I can be thankful that they helped me then, but still move on, and learn other methods.