What are the warning signs which show that your drowsiness is serious enough to place you at risk?

• You have difficulty focusing and keeping your eyes open.
• You can't remember details about the last few miles you have travelled.
• Your mind keeps wandering and you can't seem to concentrate.
• All of the above.
  Explanation:

  "Here are some important warning signs that your drowsiness is serious enough to place you at risk: 1) You have difficulty keeping your eyes open. 2) Your mind keeps wandering and you can't seem to concentrate. 3) You can't remember details about the last few kilometers you have traveled."