Thanks for posting here in the Google Nest Community.
I know how it feels when something isn’t working as it should. A few things: which Chromecast model are we working with? Has there been any changes in your network? How far is the device from the router? Are you using a dual band router? If so, which network did you use to set up your Chromecast?
You can do a sequential reboot. First, unplug your TV for 30 seconds, then do the same thing to your Wi-Fi router to refresh both devices and your Wi-Fi signal. Rebooting your phone will help too and make sure that you are on the same Wi-Fi network.
Check this link for more information.