Here's a poster who says he's an Oral and Maxillofacial Surgeon, a medical professional in the Navy, and that he "addicted" to paintball. He talks about injuries of paintball to the neck region.
"Getting hit in the Thyroid Cartilage aka the Adam's Apple:
From a distance this will just make you not feel too good for a few min, welp, bruise, made fun of. If you were to get hit there from a less then 15 - 20ft away, it could possible casue enough damage to collapse your trachea (windpipe) or actually cause enough swelling to make you start choking. Both of these are not really that likely but could possibly happen
Getting hit in the Carotid Sheath (Carotid Artery, Jugular Vein, and Vegus Nerve) aka the side of the neck:
From a distant see above. If you were to get hit from close, you could disturb the Carotid Basal Bodies, which are partially responsible for regulating blood pressure. Depending on the damage, your BP could go up (massive headache) or go down (really dizzy, possible faint). If the Carotid Artery was to become damaged, you wouldn't immediatley know it becasue the opposite side would provide enough blood to supply the brain. Within about 5-10 min, you would have a hematoma (massive swelling of blood) in you neck which would probably begin drainging into you chest cavity causing difficulty breathing a decreased heart function. If your Jugular Vein, you would instantly know it becasue your Blood pressure would begin rising and the same Hematoma formation would begin. If the impact were to casue any type of Nerve damamge, you could possible get heart palpitaitons, or difficulty breathing
Either injury could possibly cause death if the impact is placed in the right location, from the right distance, at the right FPS. History shows us that no one has died from these types of injuries but the question was asked and I thought I would give a fair assesment"
http://www.pbnation.com/showthread.php?t=2561719&page=3
NOTE: I have no idea if this poster is telling the truth or not and IDK if we can take his words at face value.