I woke up and turned the computer on and there was no internet connection. Similar second machine not affected (hence, I can post here).

Looking through network settings, my normal Ethernet interface seems to have lost it's settings. It is now an unidentified network. I have tried entering some parameters, but I am not really understanding what I need to do.

The solution is to just refresh the parameters for the TCP addresses and parameters. Net addresses, router IP, etc. If not using DHCP, just go through the various fields with your local IP addresses.