You might have some problem in your ears or eyes.this condition is called vertigo
if you have infection or swelling in the ear causes vertigo while nodding your neck or turn the neck.
Some time due to postural hypo tension vertigo is there.
if you are above 35-40 due to cervical spondilitis you may get dizzy while doing neck movement.
So evaluate your case and take the treatment.
ok and bye.