I've worked in a few places where the stress can be very great. Looming deadlines that have the ability to cost the company money, disrupt thousands of customers etc etc.

Of course everyone has different limits and tolerances, however what works best for me is control. I don't have to be in control of the process going on around me (although' I prefer it), however I need to have control over what I am responsible for. I like to get excited about things, and that's ok to a certain extent, however what I don't want is to get in the position where my thought process is chaotic, I'm reading every 5th line, not thinking clearly etc, kind of like an excited panic.

I follow a very structured, analytical and systematic approach to "business", I communicate frequently, and perhaps ironically, slow things down when approaching a tight deadline. I like to keep things slow to keep control and stop the excited panic. Of course slow is a relative term, its not like I'm sitting around doing coffee and the like. I'm also not always after the gold plated solution, just the best and most efficient way to reach the target.

So, slow things down, communicate, and take/keep control of what you can.