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: 
A flashback is an intense example of this. When a person has a flashback, they involuntarily re-experience a moment from their past, sometimes in such great detail that they don't realize it's only in their head.

The experience is typically triggered by a familiar or related sensation, e.g. smelling a peculiar odor that was present at the time the memory was formed.

A true flashback is normally only symptomatic of disorders like PTSD, or facilitated by psychoactive substances like LSD. However, if you interrupt someone who appears lost in thought, they might make the casual excuse that they were "flashing back" in response to a familiar song or some other nostalgic stimulus. Their exaggeration alludes to the tendency for a flashback to remove a person's attention from reality, as theirs appeared to have been.
There is not a single word in existence that describes this action of the mind. Automatic reflection may be a useful description.