Stress
If you're of the engineering mind, then all the math and science you'll have to do will be a piece of cake—or Pi (#mathjoke). The stress will come from problems that arise while testing your math and science skills in fuel cell form. Research and development is a lot of planning and know-how, coupled with a fair share of trial and error as well as a smattering of on-the-fly fixes. You may spend weeks working on one bug in the system, only to find that you kept accidentally triggering the off switch. So much for that Hawking-level brain of yours.
A different kind of stress comes from outside forces: project deadlines, specifically those set by anybody other than the engineers actually building the dang thing. As with any development project, the reasons behind creating or improving something are not just Will it help humanity? or Will it solve a problem?, but also How much money can we squeeze out of it?
Sometimes, especially in business, the last question is the one that gets asked the most. The company you work for or the client that funds you will expect results, and often those expectations will be, like, a month earlier than you can manage.
That's okay; at least with the amount of overtime you'll be putting in, you'll be able to enjoy all those extra numbers. We're talking, of course, about the extra math and physics you'll be doing. Did you think we were talking about money? You're salaried, silly, there's no such thing as overtime pay in your line of work (although you'll probably be able to deduct all the extra coffee as a business expense).