Rolling your head around and toward the back of your neck may be in your regular movement practice (and feel good), however, there are some risks to be aware of. Dropping the head back increases the risk of vertebral damage and stroke. There have been reports of injury in cervical hyperextension including joint damage, impaired blood flow, and stroke. Be especially mindful during salon hair washing as the neck is in this vulnerable position. The risk is increased as we age, though women in their 20s-40s are having strokes. Some risk factors are smoking, pregnancy, migraines, and the use of birth control.
To mitigate any risk, during yoga classes I always teach the three finger rule. Put three fingers on the back of your neck and gently shift the head back. When you reach the place where your fingers are crunching together…that’s when to stop moving back.
Reference: Science of Yoga by Ann Swanson