guinea pig found lying down, cant stand up, arches neck right back when picked up

Question
Hi
I found my brother's guinea pig lying down in his run on her side. He was trying to stand up but couldn't. I picked her up to bring her inside and she arched her neck right back. She is now lying down but she keeps trying to stand up. She isn't squeaking but is struggling and looks like she's in pain. I have seen this before in a couple of my rabbits, both of whom died.
Does anyone know what has happened? Is it a broken back or neck?
If anyone can help I'd really appreciate it

thanks
Emily :(

Answer
WHEN ANYTHING SUCH AS THIS HAPPENS, TAKE YOUR ANIMAL TO THE VET IMMEDIATLY!!!!!!!!!!!!!!!!!!!! If you do not have a piggy vet then go to http://www.vetlocator.com/advancedsearch.php under ('pet type' choose 'pocket pets' for 'distance' choose 5 miles and work your way further if you have no results.