If in the past you suffer any form of abuse, which is generally inflicted through being a victim of a violent act or most common in our culture is to be through being lied.
We experience emotional pain whenever we lose something, like when someone close to you dies, at the end of a relationship, or when you lose money etc. The purpose of violence and lying is to create a win lose dynamic where the person that inflicts the abuse gains something from the other person in an unfair way. This is why abuse causes emotional pain, when emotional pain occurs we all have a coping mechanism. For some people that is drinking a glass of wine, eating chocolate or chatting with a friend.
When the abuse is allowed to happen for a long period of time everything becomes chronic. What we call that coping mechanism when it becomes chronic is mental illness. All what mental illness is an attempt to control emotional pain regardless you are talking of depression, anxiety, ocd, bipolar etc.
Even after the abuse is over and if you are not being harmed anymore, first of all there will be some confusion that will make you sabotage yourself that you need to clear up, but there it also will be emotional pain that comes out of your memory.
This is a mechanism that your body has in order to protect you from repeating the negative experience you had in the past. Sometime the pain is so intens that the person that experiences it will become absent minded and engage in some sort of pleasurable activity to distract themselves from the pain this could be everything from smoking, any other drugs, to more subtle things like daydreaming or absent mindedness. If you are as bad as I was you can have memory issues so bad that you could hardly remember what you did for days.
This type of distraction makes you a poor performer in life it makes it hard to concentrate or be consistent in your actions, it also can make you hard to be around. This is why people who suffered from abuse struggle with relationships and in their career.
Which is going to lead to a vicious cycle where in certain situation based on your negative past experience is going to bring emotional pain to the surface that will cause you to need to cope with the pain this making you an especially poor performance which is going to lead to further loss and more negative and painful experience which is going to create another painful memory.
This can make life quite unlivable, it is a vicious cycle where nothing seems to work the more negative memories you have the more negative experience you end up living.
The way out of these cycle starts with truth, by learning the truth about your situation you get a new image of what is possible to accomplish. Unfortunately your emotions are not responding to logic or reason they are mostly simple survival responses designed to keep you safe, they respond to your situation and the environment that you find yourself.
So when you revisit that situation that is making you dissociate, the intention in your head to act in a certain way is going to be one while your emotions are going to align with the past experience and contradict your intentions.
This is going to create hesitation which is crucial, we don't want to avoid hesitation we actually want to create it because through hesitation is how your brain relearns. You might find yourself going back and forth and pausing a lot if you are patient enough you will eventually reach the point of relief where your emotional pain is going to decrease dramatically.
Which means that you are much likely to perform well when you are not under emotional distress which is going to create a positive memory of you in this situation.
And when you have a big enough history of positive memories there will be no need for your body to warn you of any potential danger. So you will stop dissociating!
There is no way of erasing the past, the only way out is forward, by creating new positive memories the past loses some of his emotional charge so you can claim back your life and live a full life.