What about 'War of the Worlds' syndrome? Perhaps you're concerned about liability for frightening the easily-persuaded populace with your fiction. It's highly unlikely you'll run into problems. (The situation might be different if you were claiming something as true when it was not.) Anyway, as history proved in the case of Orson Welles' "War of the Worlds," few people took any action based on the so-called deception. Much of the "panic" was drummed up by newspapers, fearful of radio's encroachment on their turf.