Flow is a state of total immersion in a task that is challenging yet closely matched to one’s abilities, akin to “being in the zone.” Flow occurs when a person’s skills match the level of challenge presented by the environment and when a task includes clear goals and immediate feedback. Tasks that are too easy are boring. In contrast, tasks that people perceive to be too difficult lead to anxiety.
Some individuals are more likely to be bored than others. People with a strong need for novelty, excitement, and variety are at risk of boredom. These sensation seekers (e.g., skydivers) are likely to find that the world moves too slowly. The need for external stimulation may explain why extroverts tend to be particularly prone to boredom. Novelty seeking and risk-taking is the way that these people self-medicate to cure their boredom. 
Absent-mindedness is where a person shows inattentive or forgetful behaviour.[20] Absent-mindedness is a mental condition in which the subject experiences low levels of attention and frequent distraction. Absent-mindedness is not a diagnosed condition but rather a symptom of boredom and sleepiness which people experience in their daily lives. When suffering from absent-mindedness, people tend to show signs of memory lapse and weak recollection of recently occurring events. This can usually be a result of a variety of other conditions often diagnosed by clinicians such as attention deficit hyperactivity disorder and depression. In addition to absent-mindedness leading to an array of consequences affecting daily life, it can have as more severe, long-term problems.

When the antiproton was discovered … it sent a wave of ennui through the physics community. Not that its discovery was unimportant, but on the basis of Dirac's theory, everybody expected it. — Roger G. Newton, The Truth of Science, 1997 Chauncey and I were keen enough about our aesthetic solution to the ennui of war to try to proselytize others. He organized discussion groups with the crew; I took volunteers to visit landmarks … — Louis Auchincloss, "Atlantic War," in Authors at Sea, ed. Robert Shenk,  1997 The attendant outside was standing on tennis balls, exercising the soles of her feet, her body swaying back and forth with the ennui of jelly. — Edna O'Brien, New Yorker, 17 June 1991 Thus the days of life are consumed, one by one, without an object beyond the present moment; ever flying from the ennui of that, yet carrying it with us … — Thomas Jefferson, in a letter dated 7 Feb. 1787 Thomas Jefferson: Writings,  1984 the kind of ennui that comes from having too much time on one's hands and too little will to find something productive to do