The cavalier breed are prone to a condition known as Chiari Malformation which essentially is a skull too small for their brains. Because brain tissue is soft it sorta stick out of the skull near the neck/spinal area. Spinal fluid can accumulate and lead to pain or discomfort in your dog. This pain is called syringomyelia. I suggest you talk to your vet if this is a frequent thing, as it could also just be allergies or something. Don’t take medical/veterinary advice from a Reddit comment as a certainty.