To use an outdated term, something is stressful if it impacts your superego—whether or not there is a real person expecting some property X of you, the need to be/do/have X has been wired into you, through socialization, as a terminal goal that you must reach in order to be happy. Alternatively, something can be stressful if it impacts your id (I use this term more for parallel structure than utility): you can instinctually crave X (such as high-calorie food, or sex, or status, or survival in the face of near death.) And either one will cause X to be considered stressful along with as any pursuit instrumental to achieving X, however many levels removed.
On the other hand, if you can draw a line in your hierarchy of instrumental goals and say "goals below this line do not affect pursuits above this line, except in-so-much as I decide it to be so (through a bet or somesuch)", then you partition the stress into the hierarchy above, and create leisure in the hierarchy below. In game design, this line is termed the http://en.wikipedia.org/wiki/Magic_Circle_(synthetic_worlds) .
Of course, something can be both leisureful and stressful: if you take a stressful pursuit and then add the pursuit of mastery within it, you can usually make it feel like (stressful) fun. The pursuit of mastery is simply the push, for its own sake, to work at a higher, and more quickly increasing, level of skill than you would if simply working for consequence; because of this, mastery sometimes overwhelms the need to recognize the consequences of the work at all, at which point the work becomes leisure (i.e., if you practice until you are winning tournaments 100% of the time, the consequences of losing a tournament cease to matter. If you grind levels in a video game, the bosses cease to matter. And so on.)
If you want to get more done at the expense of stress, you can easily find some way to attach your goals to a parent goal that will embody such stress into them. Make the affections of a member of the opposite sex dependent on completing your goal, for example (find someone who thinks chiseled abs are attractive, and set yourself to dating them => you will stress out about getting chiseled abs.) Hypothetically, if you knew this trick when you were a child, you could make your parents act disappointed if you didn't do X—that would impress into you a great desire to do X, though you would reject doing X for a period of about 10 years at some point or another, coming back to it afterward. Obviously, make eating dependent on X—this is one reason why startups can be "exhilarating."
If you want to get more done without stress, the answer is simply game design. Make the "small matter" of your goals addictive. Guarantee yourself intermittent rewards for your work (entertaining TV episode every 1000SLOC committed, without any displayed statistic for how many SLOC you have to go, only a notification when you reach it), and so forth. Remove "lame duck" periods—times during which what you're doing won't change the outcome of the "game" (won't push you toward success or failure.) Work at the edge of your expertise, such that there is always a chance of failure, but a failure that is insulated from outer failure (your refactoring didn't work out, so you have to throw away your work and start again—but you don't have a deadline, so this is okay. It just stings a bit.)
On the other hand, if you can draw a line in your hierarchy of instrumental goals and say "goals below this line do not affect pursuits above this line, except in-so-much as I decide it to be so (through a bet or somesuch)", then you partition the stress into the hierarchy above, and create leisure in the hierarchy below. In game design, this line is termed the http://en.wikipedia.org/wiki/Magic_Circle_(synthetic_worlds) .
Of course, something can be both leisureful and stressful: if you take a stressful pursuit and then add the pursuit of mastery within it, you can usually make it feel like (stressful) fun. The pursuit of mastery is simply the push, for its own sake, to work at a higher, and more quickly increasing, level of skill than you would if simply working for consequence; because of this, mastery sometimes overwhelms the need to recognize the consequences of the work at all, at which point the work becomes leisure (i.e., if you practice until you are winning tournaments 100% of the time, the consequences of losing a tournament cease to matter. If you grind levels in a video game, the bosses cease to matter. And so on.)