When you stall on a brief summary, step back and keep it simple. If the paragraph isn't large or complex, neither is the summary. Neither is your anticipated test question.
Don't try to do this a couple of nights before the test.
Don't do this method for more than an hour at a time until you've adjusted to it.
Yes, It Really Works
I used this method, recently, when I was teaching from a textbook I had never read.