given you are not triggered in any way -

from your post -

"I'm not overly anxious (any more than normal ), my blood pressure is fine, I've eaten well and it doesn't get affected by food, and I have no other symptoms or pain. I actually feel kind of amused while it is happening"

and

"just like when I was a little kid and would wear my Dad's strong glasses and try to walk around in the yard. "

Then its most likely not DID related. A person dissociates into altered memories by dissociating to get away from a problem that is upsetting them. they are triggered (upset) by something in their life - they see, hear, taste, smell touch or are touched by something some one that reminds them of an unconcsious memory. unconscious memories are memories that are stored at a level of thinking that the person has no awareness of.

If this was DID related you would have no memory of putting on your fathers glasses and how it made you feel.

you would be acting out the memory WITHOUT being aware of why you are doing so and usually without being aware that you are even acting out a memory.

And even then you would most likely not know what you have done or that its from that memory of putting on your fathers glasses. Someone in your present life would be asking you if you are alright because you walked like you were drunk the other day kind of thing.

or you have worked in therapy and you remembered that memory while remaining co conscious (in that light headed foggy off tilt way) and in which case because you now know where the memory is coming from you no longer experience feeling like that when remembering the memory of putting on the glasses because being co conscious while the memory replays restores that memory in the conscious level so that you no longer have to be dissociated to think about that memory and feelings. basically you would no longer be acting out that memory.

In the second situation - the driving the car if something upset you right before the situation happened yes it is a DID situation. something you experienced made you remember being in a car so you felt little. but the shrinking feeling a person cant litterally shrink from adult to child and feel themselves shrink so that part Im not sure about. I have never felt myself shrinking during a switch and neither have anyone that I know with DID. and professionals have never told me about a shrinking sensation or even asked me about a shrinking sensation so I don't think that is part of switching.

I know that when i take certain medications I can feel a shrinking sensation when I am doing my relaxation visualization that said "sink into the support you are sitting on so that you are in a comfortable position" But other then that I don't experience a shrinking sensation.

Other than the shrinking sensation yes this is what it is like being co conscious, you recongnize a feeling and have control of stopping it and grounding yourself back in the here and now so that you are no longer acting out your memories. you can think and talk about them just like a normal memory with out acting them out.