Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
It sounds like you are having several symptoms, some related to your neck and face in addition to left arm numbness and some more generalized symptoms. Without the ability to obtain a full history and examine you, I can not give you a diagnosis, however I will try to provide you with some information regarding some possibilities that come to mind.
The causes of neck pain could generally be divided into muscular problems and spine problems. Problems in the neck muscles could be related to a sprained muscle, which often results from sudden movements, incorrect postures, etc. Problems in the spine could be related to problems in the bones of the spine which are called vertebra, most commonly arthritis. Other spine problems occur when the tissue between the vertebra slips out, what is called a herniated disc. Problems within the spinal cord itself can also lead to neck pain. It sounds like your MRI has been read as negative, which makes this less likely.
If you get involuntary movements of your neck and face, as determined by your neurologist, one possibility is called cervical dystonia, in which there is abnormal involuntary contraction of the neck muscles leading to neck turning and pulling. This can be diagnosed by a neurologist if he/she sees these movements, in which case there may be a treatment for them. Also, on neurologic examination if a neurologist sees the face and eyes pulling in a particular manner, one possibility is hemi-facial spasms, a condition in which there is abnormal involuntary contraction of the face muscles. There is a treatment for this should it be diagnosed as well.
Problems in the neck muscles can sometimes cause a type of room-spinning dizziness, what is commonly called vertigo. Treatment for this may include physical therapy and certain medications.
The out of body sensation is difficult to really interpret, a more detailed history is necessary. However as you mentioned certain metabolic abnormalities like low blood sugar, blood pressure fluctuations, and some neurologic diseases may be the cause. Anxiety/panic attacks may also sometimes cause similar feelings.
Other causes of neck pain/headache will be discussed below.
Cervicogenic headache is a headache that is "referred" to the head from bony structures, muscles, and other soft tissue in the neck and shoulders. Symptoms are usually one-sided and include: precipitation of head pain by neck movement or awkward neck positions, head pain when external pressure is applied to the neck or occipital region, restricted range of motion of the neck, and neck, shoulder and arm pain. Treatment for cervicogenic headache includes physical therapy, medications, behavioral therapy, and other modalities.
Occipital neuralgia is caused by irritation or injury to two nerves that run from the upper neck to the back of the head. The irritation could be due to neck trauma, pinching of the nerves (by muscles or arthritis), and other causes. Symptoms include a piercing sharp pain that travels from the upper neck to the back of the head and behind the ears. It is usually a one sided pain but can be on both sides of the head. Treatment includes physical therapy, medications, and in some cases injections, "nerve blocks", during which a physician injects the irritated nerves with an anesthetic.
A concerning cause of neck pain associated with headache is a dissection: a small tear in the blood vessels that travel up the neck to the brain. This can occur spontaneously in people with certain conditions that affect the blood vessels, after neck trauma, or after chiropractic manipulation of the neck. The pain is often but not always associated with some sort of neurologic deficit as a dissection can often lead to a stroke.
Serious symptoms in a person suffering from neck pain that warrant evaluation by a physician include severe pain, shooting pain, or pain that spreads down the arm for example. Symptoms that require immediate evaluation include weakness in any extremity or loss of sensation or bowel or bladder dysfunction (ie not making it to the bathroom in time).
It is a good idea for you to see a neurologist soon, at your appointment he/she will be able to obtain a history and better localize your problems and hopefully offer you some relief.
Thank you for the opportunity to answer your questions, I hope you find this information useful, good luck.