Coma is not a disease but a condition, which can be caused by many disorders.

• Onset time: When a patient suffers a hemorrhage stroke or severe head trauma, coma may start suddenly. While for a person with alcohol abuse or some kind of drugs, the progress of unconsciousness may be slowly.
• Antecedent symptoms before coma, depending on the underlying disease: If the coma is caused by alcohol abuse or some kind of drugs, patients may experienced mildly confusion, drowsy or personality change in the beginning. If the underlying cause is a brain infection, patients may show signs including headache, fever, or dizziness before the actual coma develops. In some cases, coma may happen so quickly that patients or their families don’t have time to notice.
• Signs of coma

• Loss of consciousness
• Some spontaneously movements, including shaking, tremors, and jerking movements.
• Eyes’ abnormal movement
• If the breathing muscles are affected, the patient may show irregular breathing.
• No response to external stimuli

Diseases with similar symptoms are:

• Syncope
• Epilepsy
• Dizziness