Unlike the solution which most Webmasters use, I host this site on my home computer, running as a server. But my IP addresses are dynamically-assigned and owned by my ISP, which is allowed to switch them from time to time.
Therefore, I have software which is meant to track such a switch, and to update the new IPs to the public DNS server pool. That service happens to be called “DynDNS”.
Just this morning, from about 4h00 to 12h00, the Web site was not visible. The ISP had made a routine change to my IP, as they have done many times before. But this time, DynDNS casually failed to track the change.
The IPv4 and IPv6 addresses are up to date currently, due to my human intervention. Therefore, my site should be publicly visible again. I apologize for any inconvenience.