Thank you for the good wishes on the foot. I appreciate it a lot.
It looks like I have a stress fracture in my foot. The pain increased a lot today, and my foot was swelling over my shoe like bread in a loaf pan, so I decided to see a doctor, which involved much fussing over the internet on account of the fact that I've never gotten around to getting a primary care physician and needed to find someone in a hurry.
I have to see a podiatrist to confirm - apparently these things don't always show up on x-rays - but for now, I have to stay off the foot as much as possible. It can take 6-10 weeks of healing before you can run again. So Vegas might well be out for me this year.
I had no idea just how much I love running, and love the progress I've been making; I had no idea how important running this marathon is to me, or how much I love connecting with fellow runners on the Web, until I sat this afternoon watching fat salty tears fall beside my foot on the x-ray mat.
"Your foot must hurt a lot," the technician said sympathetically.
I'm lucky that I rarely stay down for long, and I'm sure that in a day or so I'll be feeling positive again - plus there's a chance that the podiatrist might have a different view - but I have to admit it: I'm feeling pretty low right now.