If you fall asleep within 5 minutes of lying down, you are likely to be suffering from severe sleep deprivation.
This is also true if you feel drowsy throughout the day. Even if whatever you are doing is boring, it should not cause to you become tired. Oftentimes, sleep-deprived individuals experience brief episodes of sleep throughout the day called ‘microsleeps’ - frequently they are not even aware these episodes are occurring! We in the modern Western world are not typically very knowledgeable on this subject because severe sleep deprivation has become such a normal part of our everyday lives!