I have a herniated c5-6 disc, how common is this, how can it be treated, and can it become fatal if not treated properly?

Common. Neck and low back disc problems are very common. See them almost daily. Very treatable with many options. Usually start with physical therapy. Epidural steroid injections in the neck are often used if surgery does not appear necessary, especially if pain or numbness go down an arm. Not fatal. Usually a broken neck is the only fatal injury to be concerned with, not a herniated disc.