You're definitely not stupid Mr. V

I've graduated University and still find myself 'gapping out' during lengthy and ambitious readings (as the above poster also mentioned).

The lack of comprehension I find usually comes from too many thoughts in my head at the time...If I've just read a very dense chapter and continue reading I may have to take a break, make some tea and review what I've read...I may require further (supplemental) readings to explain specific concepts. (Specific subjects often speak their own language making it hard for initiates to comprehend material right away). Look up terms online or head to the library to research a bit more on the things you don't understand. Also, note, if it is a translated text from a different language you may want to consider a different translation if it is available (I've run into some interesting translations lol).

I will find myself attempting to learn new things and will run into those very cryptic moments; no matter how many times I read the paragraph nothing sinks in. Certain antidepressants and medications can sometimes impaire memory functioning over time and I know this is the problem for me. Also, stress impaires brain function. Look into possibly taking some Omega-3 supplements if you feel you need an extra brain boost they can help big time and I can speak from experience.

Also, the brain (thus memory) can be strengthened like a muscle, so it's not a matter of being stupid /smart it has to 'work out' regularly. Sometimes I do math/ word puzzles, IQ and memory games to try to keep my brain sharp. (This doesn't always work lol).

Also, you mentioned learning style...which is huge. I don't know quite the specifics of it but there are quite a few styles.
Try taking a few online quizzes to figure out what your learning style might be and the best way to approach this little speedbump you're experiencing:

http://www.wright.edu/~carole.endres/learnstyles.htm

http://www.edutopia.org/multiple-int...ng-styles-quiz

Just remember the last thing you are is 'stupid'