According to Oricon (via MyAnimeList forums), Yazawa Ai is suffering from a sudden and unexpected illness that requires some significant time off for treatment. As a result, publication of NANA will be suspended for the August issue of Japanese magazine Cookie. Japanese readers will have to live without their regular dose of super drama manga for a little bit, oh no!
Silly throw-up jokes aside, here's to hoping her illness isn't anything serious. You can't be too careful nowadays with that crazy Swine Flu going around.