it's going to be all about dat sweet sweet gradual collapse
rumors and news reports of drug-fueled maniacs attacking people randomly, the occasional riot, trash piles up, people stop trusting the government, emergency services' wait times increase until they eventually stop showing up entirely, public transit breaks down, sections of the city become inaccessible owing to police action against "criminals"
then the supply chain starts to come apart at the seams, grocery stores' shelves empty, pharmacies stop getting stocked, hospitals fill up, water treatment starts to fail, trash pickup fails entirely, sewers start to back up, corpses stop being picked up, zombie sightings more common but still explained away as drug use or something else, authorities announce complete closures of neighborhoods on security grounds, boats start to be commandeered by authorities and are few and far between
more zombies, people aware that something is seriously wrong, with ongoing disinformation, then brownouts, temporary and then permanent loss of phone lines and internet, people try to leave in droves but just cause gridlock which is never resolved, gas stations are exhausted, natural gas lines run dry, cable and radio stations start to go offline and leave only prerecorded government messages
zombies everywhere, power goes out, water goes out, civilization has collapsed
could we do all this in a single week? sure. should we? i dont think so. gradual is the way to go 100%