Full details about Vergil's Downfall! Spoilers galore!

[SpawnShooter]

Vergil's Downfall isn't a physical thing. Vergil goes into a coma after getting stabbed and undergoes a metaphysical journey to reclaim his power.

But it wasn't all in his head, else he wouldn't have been able to command the demons after.
That implies, although not necessarily physical, that it actually happened to some degree and that it wasn't just a personal journey.