I want to thank everyone for the great ideas!
* I've begun to implement the <10 minute idea as a context (I use Vitalist, so I can have multiple contexts for one task without too much trouble). Seeing a list of things that I can knock off quickly is inspiring for me-- and has already helped to curb my sense of overwhelm.
* The discussion about someday/maybe has also been helpful. I think I've been using my someday/maybe as a black hole. Things that go in there rarely see the light of day. So, I end up piling up my next actions list -- and, well, I get overwhelmed by it. I can see how dusting off the someday/maybe list might help me keep my list for the week in manageable shape.
* Also, in reading through the wise suggestions here, I've seen something with my system that isn't working so well. I have a hard time with the processing phase. I'm a good collector, but when it comes to getting everything out of my GTD list inbox, voicemail, email, and mail, I have a hard time keeping up. I often feel like I have time to either do something or process the stuff that's coming at me. I'm hoping that, once I get through some of the <10 tasks, this won't feel like an either/or scenario anymore, and I'll be able to both do and process with more regularity.
Thank you again, for all your help. I can feel my blood pressure decreasing already!