VOY S3E2, “Flashback”: Tuvok suffers an acute PTSD attack, but it's related to a memory he's pretty sure never happened. The framing story is a pretty transparent excuse to flash back to the events of “Star Trek VI” in time for the 30th anniversary of the franchise, but I'm not mad about it.
It's not as good as the other 30th anniversary episode – “Trials and Tribble-ations” – but it's still good, and Sulu and Rand aren't in that one, so this was a nice way to ensure everyone got to be in an anniversary episode. And it's cool to get some deep Tuvok backstory.
The idea of trauma as a pathogen is pretty cool.