[goodluckchuck]

If humanity in 4,000 BC lost 1,000 years of technology, then things might very well be the same today.

If humanity in 1900 AD lost 100 years of technology, then it would be very noticeable, but would not threaten extinction.

If humanity in 2022 lost 50 years of technology, billions would die.

To me, singularity is when humanity relies on the present advance of technology, were any stalling would collapse the entire species.

Snowpiercer (2013) involves this sort of thing.