Please don't ever let anyone do that again. The two vertebral arteries that supply blood to your posterior brain (occipital lobe, cerebellum, medulla, pons) are encased in your cervical/neck vertebrae transverse processes. Quick manipulation of your neck with a "jerk" can injure these arteries and lead to dissection and infarct of your brain with permanent loss of function or it can even kill you.
I've survived a vertebral dissection caused by neck manipulation which lead to permanent loss of vision.
A dissection is injury to the inner lining of a blood vessel leading to clot formation over the tear. The clot can entirely obstruct the lumen of the vessel or parts can break off and obstruct downstream vessels leading to infarct.
Please don't let anyone manipulate your neck in the future.
Here's a cohort study supporting your doctor's advice to you.
And just for some Pop culture connection - here's a link to an article about a Playboy model that died after a carotid dissection due to neck manipulation by a chiropractor.