Please post the contents of the emulog.txt file after the problem occurs. The file can be found in "My Documents\PCSX2\logs" for the installer version or in "PCSX2\logs" for the portable/binary version.
Please make sure to enclose your emulog in code tags like so (remove the empty space on the closing code tag!):
[code]
Pasted emulog goes here
[ /code]
Either overheating or some power saving plan is active
Echoing vsub, sounds a lot like thermal throttle or bad power profile. Make sure your laptop is on High Performance, and check your temperatures, before, during and after the slowdowns. I believe most Intel Core CPUs for laptops start throttling around 90 or 95 C, so try to look out and see what numbers it hits when it slows down.