Frequently my ISP will be relocating or installing new fibres and screw up the internet for the whole country.
You can try using Speed Guide’s TCP Optimizer (http://anonym.to/?http://www.speedguide.net/downloads.php).
Vista, Windows 7, Windows 8 are best set to "Default" values.
The "optimal" are not at all "optimal" for Vista and later.
"Optimal" is ideal for Windows XP.
I would name the other OS’es but no one uses them.
Anyway the issue mysteriously stopped yesterday. Might have just been a one time thing :3.