Two points on GTD that deal with this:
- Part of writing everything to down is to get it out of your head so you don't worry about it. If you have a bunch of big detailed lists and a lot to do, you don't have to get stressed out over it. That's frequently a hard choice for many to make, and the review process/50k foot view in GTD can help with this.
- GTD also encourages self assessment of what you feel up to doing. You need to be aware of what jobs you'd undertake given your amount of time and energy.
Treating GTD just as a way to empty the mind and organize your tasks is only a small part of the entire system. Half implementing it can definitely be more stressful than fully embracing some of the concepts.