This is not only a warning against flashbacks, which I have read elsewhere, but down a sentence level. "He turned when the gun went off" is grammatical and all that jazz, but not as good as "When the gun went off, he turned." (And if you don't think it will improve the prose, I can give no further defense except a suggestion to try it. I did, as a lark, and kept to it.)
I've been musing about it because I've recently read some works in which summary was all the reflections of a character on the events between one point and where he was then. Now, I do know that summary can be a real pain, and these were events that had to be summarized: not dramatic, but necessary to the story. But the effect of the reverie was to make them summary in the past perfect.