When things get real slow like that the first thing to do is a reboot of the modem, router, and computer. If that doesnt get results then wait a little while because it could be that they are working on something somewhere, and it will get better in a little while.

If it doesnt get better, well then it is time to find out if it is some kind of hardware problem. I would bet a reboot would probably fix it though if everything has been running fine,

You might do all the cleaning and defrag while your slow

Hope everything gets up to speed soon and it is nothing serious.