Stress
"Going postal" jokes aside, the life of your everyday postal worker isn't too stressful. Despite work on Saturdays, most postal peeps are expected to work eight hours a day, five days a week. And guess what? If you work more than that: overtime. Can anyone say, "time and a half?" Everybody wins. Except for maybe the USPS as a whole, which is sort of choking to death beneath strangling vines of pure, unadulterated debt. But anyway, yeah. Everybody wins.
For the most part, your biggest worry should be the monotony. Even though simple tasks are exactly that—simple—when you do them over and over and over again in the same place, it can get a bit like Chinese water torture for the wrong person. But if that's not a problem, then expect to enjoy the Zen-like thrills of sorting mail and putting it in little boxes without the risk of a nervous breakdown.