Simon T.:
A few years ago I started to occasionally do a brain trick that look pretty much like a form of meditation. Basically, I would close my eyes and "listen" or "watch" what arise in my mind. I would close my eye and wait for a memory (or some very basic idea but definitely not complex thoughts. Mostly things that take the form of an image). I would then avoid creating a "story" with this memory, In other words, I would avoid active thinking. I would try to avoid as strongly as possible to not think of this memory and instead go back to watching what arise in my head. When I say my head, I really mean my physical head. I would pay attention to what go on in the frontal lobe (well, that's how it feel).
Your meditation is called: vipassana.
What you did do is: being mindful of thoughts and images which arise in your head. You noticed them, but didn't note them (by labeling, e.g. "critical thought"). This is all perfectly fine.
You did this to the exclusion of everything else. You could try and incorporate noting/ noticing of everything which enters your consciousness to make your vipassana practice more effective if you like.
See here:
http://thehamiltonproject.blogspot.com/2011/02/yogi-toolbox-detailed-noting.html
Simon T.:
The next memory that would comes would generally be connected in some loose way to the first one. I would then feel that I'm navigating a web of interconnected ideas. I could remember the face of someone, it would then bring the memory of a bakery where we meet, the smell of the bakery would bring the memory of my mother, and so on.
This could be yourself realizing the second nana = Cause and Effect.
Simon T.:
I would do this when my ADHD symptoms were really bad. In other words, when my head would be spinning out of control. After doing it for 5 to 10 minutes I would feel a brain zap in my head. This zap feeling (which is an actual physical sensation) is pretty similar to the brain zap you can experience while tapping off an antidepressant.
After the brain zap my mind would feel much clearer.
Energetic discharges in the body, explosions in the head region could be the fourth nana = A&P. The subsiding of ADHD symptoms could be caused by the release of catecholamines, which, in my opinion, are being released in larger quantities during the a&p which lead to ritalin like effects.