Thanks for the responses people.
I'm not using much webGl and my computer isn't that old, so I didn't think it was that.
As for add-ons in Chrome - no, no recent ones and none updated recently either from what I would see.
For, for posterity, funny thing is when I put the power cable back into my laptop, it all proceeded to speed along like before again! So the problem was running off the battery rather than the direct power. Strange. I just hope it doesn't turn up in the final game - Ludum Dare 28 here and I've only got 4 hours to go!
Thanks again for your time!