I think you would have been better off breaking the task down to smaller sections. 10 minutes at a time would have been easier to handle. Especially as a beginning photoreader. Staying at the relaxed level for a whole 45 minutes... flipping pages - wow or ow?. I prefer to break it down to more managable levels to allow my mind to process it... the headache? I for one would not discount the possibility of a connection. It's a bit like going into a workout and then overdoing it... the brain is often referred to as a muscle so...
As for words not popping out... you typed a nice collection of words... have you thought of guessing the position of any of them in the dictionary? When you say words are not popping into your head... do you expect them to come to you in some unusual way? Just think of a word and then imagine where it's located in the dictionary, look it up and see how right you were. Once you've started playing the game that way, then unusual words can start 'coming to mind'. If you let them *pop* then they're gone before you've had a chance to consider them 
Alex
