According to Stephanie Watson for HowStuffWorks, patients come out of comas in a variety of ways, and the signs they exhibit vary from one person to the next. Patients who lapsed into a coma because of a drug overdose or diabetes often emerge from their coma relatively suddenly once their body chemistry returns to normal. However, most coma patients exit the unresponsive state gradually over the course of several weeks.
Often, as a patient emerges from a coma, he does so by becoming conscious for brief periods of time or by moving about. These episodes of consciousness often alternate with periods of deep sleep. Doctors monitor three different aspects of a coma patient to quantify the depth of the coma. NHS Choices explains that these aspects are the degree to which the patient opens his eyes, the degree to which the patient responds verbally to commands and the degree to which the patient moves voluntarily in response to commands. A number is assigned to each of the three categories, and the sum of the three is compared against the Glasgow Coma Scale. The higher the score, the better the brain is functioning and the more likely the patient recovers.
According to Watson, 87 percent of patients who score between 11 and 15 points within 24 hours eventually wake up, while 87 percent of patients who score a three or four on the scale enter a perpetual vegetative state or die.