It probably has to go down as 'one of those things'. Routers can get into this kind of state after the connection has been up for some time, as a result of running out of internal memory or something like that. As it happens, I had a similar experience a couple of nights ago. Generally all you need to do is reboot the router.
If it happens again, you could check if it's a DNS problem by opening a command line window and typing:
ping bbc.co.uk
followed by:
ping 212.58.241.131
If the first command times out but the second one works you have a DNS problem. If both commands time out you've simply lost your internet connection.