What can psychological fatigue make you feel like?

Mental fatigue can be considered a real health disorder, and is defined as the inability to maintain an optimal mental and cognitive performance. It's also called exhaustion or tiredness, and it also decreases the optimal physical performance. Although one of its symptoms is sleepiness, the two conditions shouldn't be mistaken, as sleepiness could be temporary and probable the result of a lack of sleep or adequate rest and fatigue could be considered a chronical condition.