There is no great "falling away". It's either the "catching away" of the church during the Rapture. Or it's referred to as "the rebellion" when the antichrist starts the Great Tribulation by signing a 7 year peace treaty with Israel.

When you study other passages about Christ's return you'll see that Jesus says that he will return when no one expects him. Yet once the antichrist desecrates the Temple it will be 1260 days until his return. So it should be obvious that we're looking at a pre-trib Rapture.