You will need to give a bit more information like;
What is your set up (computer, wifi or wired, OS etc)
Have you checked your broadband speed hasn't dropped etc? You can do that here
http://www.speedtest.net/?noflash=1 (don't click on any of the speed up my Mac links though!)
Have you tried the obvious things like rebooting your machine, router etc? Don't have as many tabs open etc?