Turns out they weren't loose -- although the locking lug nuts in the rear were missing, both of them -- so maybe the wheel is bent. In any case, now that I know that the wheel is not going to come off, I can drive it somewhere to have it looked at. (The rear locking lug nuts have been replaced, as I had the foresight to stop at the auto parts store on my way home from Coalinga.)
Or maybe not. I now have the van back.
I have music! I have air conditioning!