This is a very interesting question to me because I've worked in a few different fields. Sorry for the long response.
tl;dr: You asked how stressful your field is, but stress is a combination of many things. Your field definitely plays a part, but also your individual level of responsibility, and your work environment (e.g. how well the organization is run, how good the managers are, etc), your coworkers, and also how much you enjoy your job.
First I spent 8 years in aerospace, specifically human space flight for a NASA contractor. I would give that stress level an 8 out of 10. I was very early in my career, so my personal responsibility level wasn't that high. I worked in various roles: quality, design, and planning, before settling in as a structural analyst (this has become my expertise over the years). I gave it an 8 out of 10 for stress level because the work was highly critical (if we screwed up, people died) and there was occasional intense schedule pressure. But at the same time, there was a strong support system, especially for inexperienced engineers, and there were a lot of processes to make sure everything was done correctly. People often complain about too much "red tape" to get things done, but having all those checks and balances help to make sure that any hypothetical miscalculation gets caught before it gets built and flies.
Next I moved to a different defense contractor building ships for the US Navy. I would give that stress level a 9 out of 10. I was a senior engineer by this point, so my personal responsibility level was much higher, but my rating is mostly due to the fact that the specific program that I was working on was very poorly run. We were constantly over budget and behind schedule, so there was constant management pressure to do things faster and with fewer people. And this particular organization definitely took more risks, and played more fast-and-loose than I was comfortable with coming from aerospace. The critically of a Navy ship is much lower than a rocket. If we made small mistakes in the design (structurally speaking) everything would mostly be fine, but we wouldn't get the life out of the ship that was required. (For example, it would only last 10 years instead of the required 28.) Those ships are inspected often enough that any fatigue cracks would be caught and repaired before something bad would happen. But still, we had requirements to meet and we never had the time necessary to do the work thoroughly. Also the company that I worked for was constantly looking for opportunities to lay people off (that whole over budget thing). In the 5 years, that I was there, I think I witnesses 7 layoffs, usually small groups, but sometimes big groups. So yeah, it wasn't a great work environment.
Now I work for a company that designs and manufactures factory equipment. I'd give my current stress level a 4 out of 10. This work is not critical. Now I'm a borderline expert in my field, so my personally responsibility is very high. But schedule pressure is rare. The company is extremely well run and profitable; it treats employees with respect and trust. Honestly, it's great here and I really love it. Sure, it's not as cool as space ships, but this is the happiest I've been in a job.
