Cameo,
Lots of things are happening in your body as it ventures down its path of healing.
Many things occur as the nerves wake up or deal with the inflammation of surgery, etc. Muscle spasms are very common, as is the pain - sometimes even completely new nerve pain. You just had surgery - that incision is like any other cut. OUCH! Your body is trying to heal from the trauma of surgery and is getting about building your new neck, and the first step is inflammation. That usually means swelling, a sore throat and difficulty swallowing.
Brighter days are ahead. You're right on course!
Hoping you feel better soon.