The somnolence is a sleep disorder characterized by a tendency to fall asleep, showing evident signs of weariness or sleepiness. ###Causes Usually it is produced by the lack of sleep or tiredness. Although it can also appear as a secondary effect of some medicaments (tranquilizers, sleeping pills, antihistamines) or for pathological reasons: - Depression. - Sleep apnea. - Narcolepsy. - Alcoholic intoxication, opioid, barbiturates. - Liver failure. - Under-active thyroid. - Brain tumors. - Acute/chronic Meningitis, ETC. ###Consecuences Somnolence can reduce the reaction time (a critical element of safe driving). It also reduces vigilance, alertness and concentration so that the ability to perform attention-based activities (such as driving) is impaired. The speed at which information is processed and the quality of decision-making may also be affected.