Medieval life lacked precision measurement: no clocks, no KPIs, no micro-evaluation. Much of modern stress isn't workload but being quantified. That shift from 'work until the task is done' to 'work until the metric is satisfied' changes everything.
Oh, and a devil might jump out of the shadows, or a witch might kidnap your child, or a fairy, or...
I guess maybe we replaced outright fear with stress.