For most the day today, speeds have been extremely slow, with service so impaired that most of the time I cannot complete a speed test. A trickle of data seems to get through. It varies from minute to minute. There appear to be DNS problems (though that could be because data is just not getting through). Some sites seem to be more affected than others. It looks to me like router problems or DNS problems.
This also happened three days ago, though it cleared up more quickly. Today the problem is ongoing.