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.
Lethargy is a state of tiredness, weariness, fatigue, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to boredom, inadequate sleep, overexertion, overworking, stress, lack of exercise, or a symptom of a disorder. When part of a normal response, lethargy often resolves with rest, adequate sleep, decreased stress, and good nutrition.[21][22]

“When I have neither pleasure nor pain and have been breathing for a while the lukewarm insipid air of these so called good and tolerable days, I feel so bad in my childish soul that I smash my moldering lyre of thanksgiving in the face of the slumbering god of contentment and would rather feel the very devil burn in me than this warmth of a well-heated room. A wild longing for strong emotions and sensations seethes in me, a rage against this toneless, flat, normal and sterile life. I have a mad impulse to smash something, a warehouse, perhaps, or a cathedral, or myself, to commit outrages, to pull off the wigs of a few revered idols...”
“I don’t like to be bored, but without it I couldn’t escape from it. Creativity is the byproduct of escapism.⁣⁣ Inventiveness is the byproduct of laziness.⁣⁣ Productivity is the byproduct of your mom.⁣⁣ Lol. Anyways. ⁣⁣The bored do weird stuff to not be bored.⁣⁣ The lazy invent things like cars so they don’t have to ride horses. ⁣⁣Get bored to get busy.”

"Meh" is an interjection used as an expression of indifference or boredom. It may also mean "be it as it may".[40] It is often regarded as a verbal shrug of the shoulders. The use of the term "meh" shows that the speaker is apathetic, uninterested, or indifferent to the question or subject at hand. It is occasionally used as an adjective, meaning something is mediocre or unremarkable.[41]
“Time is quixotic because it can torment us. When we have insufficient stimulus to fill our lives, we resent the relentless quality of time, and we engage in activities designed to “kill time.” Time that passes slowly creates insufferable boredom; time that passes to quickly makes us aware of our accelerated death march. A person’s perspective on time depends mostly on what they are most afraid of, boredom or death.”
What can you do about boredom? Obviously, there are times when you are stuck. If you are listening to a lecture that you cannot leave, then you just need to find a way to get through it. When you have some control, though, use your understanding of boredom to help you out. If you can, try to do a meditation exercise to lower your arousal level. Also, keep some music handy. Music you enjoy can crowd out distractions in the environment. It can also influence your mood in positive ways to counteract the pain of being bored.  

The most common way to define boredom in Western culture is having nothing to do. Boredom is generally viewed as an unpleasant emotional state in which the individual feels a pervasive lack of interest in and difficulty concentrating on the current activity. The condition corresponds more precisely to the French ennui, an existential perception of life’s futility. Ennui is a consequence of unfulfilled aspirations (Goodstein, 2005).