Glad it's working now. 
What did bring it back to normal?
And to guard against future resolution failures on your PI-hole host:
Did you configure a static IP address on device?
If so:
Since you are running on RPi OS, consider adding a public nameserver to static domain_name_servers after 127.0.0.1 in your /etc/dhcpcd.conf.
This would allow your Pi-hole host to resolve DNS even when Pi-hole should be rendered inoperative for some reason.
And since you are running unbound:
If you've upgraded to Bullseye somewhere in between switching branches, it would also be worth to check Failed to start unbound - #9 by jfb
(and if interested, for a detailed background, you may also refer to WARNING: Raspbian October 2021 release bullseye + unbound).