I have a feeling Tuvok’s illness was in other episodes. It was certainly strongly set up things like murder mystery episode where he investigated himself. He had a *lot* of psyche damaging stuff go on throughout Voyager. Both were just natural enough logically for Voyagers light handed approach to serial.
It wasn't. I finished re-watching the show recently and aside from a couple random "Tuvok has issues" episodes like the one when he shared a mind-meld with Suder, the one with Mr Sulu, the one you mentioned and another when he set up a holodeck scenario or killing Neelix there is no mention that something might be wrong with him. However those episodes were few and *very* far apart (and were never mentioned again) to serve as a proper foreshadowing for his illness at the last episode.
Truthfully while Voyager's episodic approach was good for the casual viewer, it didn't help for things like a sudden relationship, deep friendships with unseen crew members that conveniently died in that same episode or an illness that was so serious that should have been a much longer storyline to be believable.