Caffeine is a stimulant that can cause side effects, especially if you consume too much or if your body is sensitive to the substance. Caffeine is in chocolate, coffee, kola nuts, tea, soft drinks and is even in some medications.

Muscle spasms, also known as muscle cramps or a charley horse, are involuntary contractions of the muscles. Although these contractions can be very painful, they are rarely dangerous or a cause for concern. However, severe or lasting pain should always be examined by your doctor.

Pulled muscle is an alternate term for a muscle strain. Either way, it sounds -- and is -- painful. In his book, "Conservative Management of Cervical Spine Syndromes," Donald Murphy, D.C., defines a neck strain as a partial or complete tearing of the muscles and associated tissues supporting the neck.

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Muscle spasms are involuntary contractions of a muscle. They are a common components of neck pain and injuries and can be the result of many different conditions. In most cases, muscle spasms are minor annoyances that improve quickly on their own or with conservative treatments.

Muscle cramps are painful involuntary contractions or spasms in one or more of the muscles lasting a few seconds to several minutes. They can occur after exercise or during the night and are commonly caused by overuse of a muscle, dehydration or vitamin and mineral deficiencies.

Involuntary muscle spasms may take the form of minor twitches or larger limb jerks. The behavior goes by a number of names, including myoclonus, muscle fasciculation and benign muscle spasms. The muscle spasms may be a mere annoyance, or they may be a sign of a serious health condition.

According to the Family Doctor website, neck pain may be caused by injury, stress, faulty posture or other health problems, such as degenerative conditions, fibromyalgia or disk herniations. One of the most common symptoms reported by neck pain patients is muscle spasm.