You seem to be saying medieval life also lacked stress. At any moment: an army could invade and feed itself off of your livestock and grain stores; a drought could guarantee mass starvation in the winter (or sooner); disease could strike down someone you love, and progress infecting others; your own livestock could trample and kill your smaller children (thus city laws against letting hogs forage in-town); you could only put by 99% of the food you will need this winter; etc.

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.