Chances are if you've been on a long climbing trip or spent more than a few hours belaying in your local climbing gym, you've experienced the uncomfortable and sometimes debilitating strain of "Belayer's Neck".
The prolonged position of looking up while belaying can cause compression on delicate spinal structures, such as joints, nerves, discs and bone, resulting in pain that keeps you from climbing.
In extreme cases, Belayer’s Neck can result in Facet Joint Pain: an irritation of the facet joints in the neck. Facet joints are parts of the bones in the neck and back which help guide motion and have been implicated as a major source of neck and lower back pain. Studies have demonstrated pain sensitive nerve endings in the facet joints' mechanically sensitive receptors which become activated with inflammation.
You can find a lot more information on neck and spine associated pain online. These are a few external sources with good information:
Generally speaking though, if you put any joint in an extreme and sustained position, eventually it will hurt. Treating extreme pain and joint damage requires professional attention. In many cases, even stretching will further aggravate the injury. The best way to avoid Belayer's Neck is to avoid the constant upward tilt of the head that long belay sessions may require.
Belāggles belay glasses allow you to see your belayer without the straining upward tilt of your head. Ask anyone who has used them on long project belay sessions or on day long multipitch routes and they will attest to the neck-saving good time.
Also, it’s always good to talk to your local "healer" (chiropractor, acupuncturist, orthopedic surgeon) to learn more about how Belāggles would help you maintain a healthy neck while belaying.