A tremor is an involuntary, continuous contraction of pairs of muscles in any part of the body that result in the affected body part shaking and also results in a lack of fine motor control. Shivering is a type of tremor caused by the body attempting to warm itself when it is cold. Other tremors, which often affect only certain parts of the body, can be the result of several conditions from as mundane as imbalanced electrolytes in the blood due to overexertion or slight dehydration to serious neurological conditions such as Parkinson's Disease and Huntington's Disease. As such, random intermittent tremors are usually not a cause for great concern, but a consistent tremor is clearly the result of a serious underlying condition.

Tremor at Wikipedia

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