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Understanding Fatigue & Drowsiness


Fatigue can be defined as weariness or exhaustion from labor, exertion, or stress. Causes of fatigue according to the Mayo Clinic:

  • Lifestyle factors
  • Alcohol or drug use
  • Excess or lack of physical activity
  • Jet lag
  • Medications
  • Lack of sleep
  • Unhealthy eating habits

Certain health conditions, such as anxiety and depression, can also cause unrelenting exhaustion and fatigue. See your doctor if you have been experiencing excessive fatigue.


Drowsiness refers to being abnormally sleepy during waking hours.

Causes of drowsiness:

  • Working long hours or different shifts
  • Not sleeping enough
  • Sleeping disorders
  • Medications

Certain health conditions, such as diabetes, changes in blood sodium levels, and more, may also cause drowsiness. Contact your doctor to determine what is causing your drowsiness or to see if your medication may be a cause. Medline Plus has more information on conditions that may cause drowsiness and how to treat it.

The Driver Drowsiness and Fatigue training module, found on the CMV Driving Safety website, provides an understanding of truck driver drowsiness and fatigue. The module helps safety managers identify the onset of drowsy and fatigued driving in the context of commercial vehicle operations, the countermeasures that drivers typically choose to combat drowsiness, and any barriers that keep drivers from making decisions that support them staying alert. The module also suggests possible measures for detecting drowsiness and fatigue and provides tools that safety managers can use to manage and reduce the occurrence of driver drowsiness and fatigue in their fleets.