[tjex]

There's no need to think badly of this. You're recognising that that culture and workload is unhealthy for your body and mind, and you're feeling like leaving. That's a good thing. It's no secret that working at Amazon has this effect on people. You don't have to site particular reasons why you wanted to leave. Just find a company that you would like to work at, and explain that you prefer their product / team / atmosphere / conditions / more (which will be true).