I do these same kinds of things when driving or reading, even just walking. I can't remember whether someone told me something or I told them something, or not.
Of course I often get up to get something, walk into the next room, and forget what I was looking for or even what room I was going to.
So part of this, for me, can be attributed to my fibromyalgia fibrofog, which involves inability to focus, concentrate, retain, remember. Yet even my fibro is a result of my SA trauma, anyway.
And I also fade off into daydreams. And then there are the flashbacks.
I think Lloydys onto something in relating this to dissociation.
I think our minds get so confused by dissociating us from our bad memories (not to mention suppressing or repressing them), that they can at times become unable to discern as to what to dissociate us from.
Of course we are not conscious of doing this I don't think. But its like we separate ourselves from past abuse memories, but we get used to dissociating and separate ourselves from our present reality, even in non-abusive situations like driving, reading, etc.
And I know there have been times when I've like gotten verbally abused on the job or been a road rage victim that I've just blanked out or shut everything out.
Unfortunately, sometimes in those instances primal emotions take over to fill in the blank, which means return the verbal attack or road rage; or lately, fortunately, its meant just walk out or move away.
Lloydy, I never thot about the learning disabilities tie-in either. Now I know why my teachers were always telling me to pay attention.
I used to sit & draw stick figures or daydream. Yet I usually retained enuf of what the teacher was saying to be able to study it and pass tests. That's what got me thru high school.
And my late brother, who was mentally & physically handicapped? I always felt he was not so much "retarded" as "learning disabled." Probably due to the same early abuses I suffered, only he was probably even younger.

I think he had a bad case of what New refers to as SADD (Sexual Abuse Dissociation Disorder)!
A good name for this problem we have: becuz its accurate, and becuz it is sad.
As an aside, I'm again amazed at the frequency with which posts relating to driving are coming up! I'm preparing one on "Road Rage On Recovery Road." (Sounds like a book title--as if I haven't written enuf books here already!...
Well, you've been warned, gentlemen!...
Wuame