Since when is this happening? How frequent is this? For how much duration this lasts? Any past significant medical or surgical history? Are you diabetic or hypertensive? Are you a smoker?
The commonest reason for this symptom is pinched nerves in the neck which can be caused by degenerative disc disease or bone spurs (cervical spondylosis). A MRI of the neck (cervical spine) would be able to diagnose the causative for this abnormal sensation (termed as paresthesia). For your age, I would also like to look in the brain also, for the reason for these feeling of heaviness. A colored doppler study of the neck arteries (called as carotid arteries), which supply blood from heart to brain will determine any occlusion or atherosclerosis in them and chance or risk of thrombus or embolism. Getting a MRI of the brain can also be considered, although chance of origin of these heaviness is more from the neck spine.
Please feel free for your follow up questions.