Any type of surgery has its risks, back surgery is no different. If you have a surgery for a herniated, or slipped, disc, the risks involve a bit more than if you were having surgery on your knee though.
Infections, blood loss, and slow healing are a few complications that are universal to most surgeries. With back surgery, there is also the risk of nerves being damaged with either pressure from blood pooling, bones shifting, or even doctor error. However, it must be kept in mind that complications like this are not usual and that, in most cases, the benefits from back surgery outweigh the risks.
You should speak with your doctor about how you feel and ask for a better idea of what types of complications may occur with your particular type of surgery.