Stargazing can be a symptom of a wide range of neurological issues. It's been known to show up with IBD and also overheating (which causes permanent neurological damage). It looks exactly how it sounds, the snake bends over backwards and just looks straight up, as if "star gazing". Here is a youtube video I found searching for "snake stargazing"....there are many more if you want to look them up.
It's bad because it is neurological damage, which is clearly bad for any species, not just snakes. It's not so much a "problem" but a symptom of a much bigger problem. You can prevent it by properly quarantining your animals, having perfect husbandry (temps especially!), and buying from reputable breeders.
http://www.youtube.com/watch?v=kKLq118HHrk