Having inattentive ADHD can be very painful. You can really honestly want to just do it. But as soon as you start, you find yourself either getting overcome with immobilizing dullness, or you simply can't help but to jump to some other "temporary" distraction like surfing the www, to get yourself perked up. Only to discover later that the whole day is shot and you've accomplished nothing.
That's more or less how I feel, except that it actually 'hurts' (the best way I can describe it) to concentrate on 'boring' tasks.