Most recently they saw a swimming pool and had to close their eyes and take a deep breath for the visual hallucination to go away.
Had another character who trailed off in the middle of talking, just staring off into space, with a muscle spasm in his cheek while he kept opening and closing his hands. He jumped when someone touched him and said he just zoned out for a second.
OH! You mean STORY flashbacks.
I use them here and there. Mostly I label the chapter "HISTORICAL ARCHIVE" or "REWIND", to cover events that I missed earlier or that couldn't be revealed prior in the story without giving away major plot points.
Used correctly, flashbacks are powerful tools that can really add flavor and life to the story.
Used poorly, they're terrible.