disclaimer: I shop on amazon, have ever since. It's this horrible catch 22 (may be butchering the use of that) of the cheapest places to buy stuff are likely cheap as one of their 'efficiencies' is that worker experience missed out the following:

'That leaderboard combined with daily reminders of 'no more than 30 seconds an item' just added to this palpable pressure to 'go go go.' I think the machine maybe even bleeped if you went over this time, again it was a haze.'

can describe my experience working at amazon.
Will start by saying I was a relatively young fit guy, and maybe more importantly low maintenance (have literally never missed a day of education or work through illness in my life) it was a one-month gig. I think it was all night shifts, can't say for sure as I think my mind has tried to erase the experience for my own sanity. Day 1 began with a slide-show which can be summarised as get ill & you're fucked. The tone was borderline intimidating.