If absolutely nothing happened, like nobody changed firewalls, unplugged things etc.... then my first suspect is a hung process. Reboot the ZD. At this point nothing is working, anyway.
If that does not fix it, go through the checklist in the article provided above. Login into an AP and ping the ZD. Even if the ping works, make sure you're not losing packets. If you do loose packets, I would look at the switch. Its ARP table, or MAC table might be full (wouldn't surprise me in a hotel with lots of turnover), either because it is underpowered, or simply hung. Reboot the switch.
Are there rats chewing on the cables? They can do a real nice job at making a cable have enough intermittent connection to keep the lights on, but the data transport is unreliable.
Is DNS OK? check to see if zonedirector.domain.tld is resolvable. This how your APs find the ZD. You can specify the ZD address in one of the APs and see if it connects.
Is DHCP working? If APs can't get a renewed lease.... they're dead. I would probably start here.....