This happens every now and then, that I read a book that's so astoundingly good, any book I read next will suck--no matter how good it actually is. What you need after a book like A Constellation is a palate cleanser. I usually rely on Terry Pratchett, but the old standbys weren't that attractive. I ended up going with another favorite author, Christopher Moore. When I need a palate cleanser book, I have to go with something I've read before and enjoyed. So I'm reading A Dirty Job, in which a secondhand shop owner becomes Death's little helper. The best books for me to read after a mind-blowing book are funny ones, I think because jokes are the perfect antidote to taking something too seriously.
Without the palate cleansers, I don't think I'd be able to read as fast as I do because I would be in regular funks from reading good books. Interestingly, the same thing doesn't happen when I read a bad book. Whatever I read next seems that much better in comparison.