As for Crusher's phaser, it was Geordi's.
Oops! I've missed that detail for more than two decades straight now.
So that leaves just one great mystery, the summoning of LaForge and Worf. Riker called for security, but security never arrived; no big mystery there if we consider the powers Quinn ought to have. But if Quinn called for Crusher to come examine Riker after the XO so inexplicably slipped and fell, why would LaForge and Worf rush down from the bridge - armed, but without
Granted, they don't rush in with their phasers actually drawn IIRC. But while Worf seems to have a weapon at hand wherever he goes, LaForge wouldn't normally be carrying a Type 2 phaser. Plenty of places where he could have picked one up; little motivation for him to do so.
How could the people who had been bugged not know?
In the end, we are left wondering what happened to the victims in general. We know Quinn is "expected to make a complete recovery", but perhaps that involves amnesia? We don't know if the people down at SF HQ died or survived (Remmick notwithstanding); Picard's worry would be justified if most of the victims met a grisly end, blowing up their starships or jumping off bridges instead of just "making a complete recovery" and reporting in with a hole in their memory. Starships blow up every second week: how many to blame on the parasites?