Mental
Fatigue
In addition to physical, fatigue also includes mental fatigue, not necessarily
including any muscle fatigue. Such a mental fatigue, in turn, can manifest itself
both as somnolence (decreased wakefulness) or just as a general decrease of
attention, not necessarily including sleepiness. In any case, this can be dangerous
when performing tasks that require constant concentration, such as driving a
vehicle. For instance, a person who is sufficiently somnolent may experience
microsleeps. However, objective cognitive testing should be done to differentiate
the neurocognitive deficits of brain disease from those attributable to tiredness.(1)
source
: wikipedia