Question: What do you call it when your mind starts examining things automatically because of being exposed to these things in the past. This is not intentional thinking nor wandering but rather an automatic response in your mind

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> John has quiet time at home and wants to just relax, but he can't stop his mind ... the events of the day.
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Using *Reflect and Review* make the thinking seem voluntary when I am trying to convey the involuntary aspect of it.

Answer: 
The word you are looking for might be '[**reminisce**](https://en.oxforddictionaries.com/definition/reminisce)' which means

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> Indulge in enjoyable recollection of past events. ‘*they reminisced
>  about their summers abroad*’
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[Oxford Online Dictionary]
"...can't stop his mind **reviewing** the events of the day".

**Review:** (*verb*) To review means to look back over something for evaluation or memory. (vocabulary.com)