Trek does literal flashbacks. You literally go back in time, or hallucinate being back in time. DS9 showed several glimpses of the Cardassian occupation, though they didn't actually show Kira participate in terrorist attacks, they referred to several specific incidences.
But, Tuvok had a flashback to the time he got that zen master logic help. Seven had a flashback to when she was a child and got assimilated. Kes went back in time to her Ocampan days. It's like after the first episode they wanted to play down the fact that Chakotay and B'elana ever did unlikable things. Only, those unlikable things are the only things that could have made them interesting.