My guinea pig is spastic?

I got my guinea pig a year or so ago. When ever you touch him, he jumps up in the air like he is having a spaz attack. I don't think it's a problem I just wan't to know why he does that? It's kind of weird because he's not scared of anything. If you walk over to his cage he wont run and hide, he'll walk over to the cage opening! My other guinea pig would always run into his plastic igloo home. I don't really know why he does this so can I have help, Why does Joey always spaz!? Thanks!