According to Restore Immune Health, nervous energy is caused by stress. The human body is designed to respond to stress in ways that protect it from threats, such as predators, as CNN explains. When facing danger or the day-to-day causes of pressure, the human brain triggers a fight-or-flight alarm, which prompts the release of large amounts of adrenaline and cortisol.
According to CNN, the heart rate surges when adrenalin is released. In turn, blood pressure goes up and the body attains higher energy levels. Cortisol is the stress hormone that boosts supplies of sugar or glucose in the bloodstream, facilitating the brain's use of glucose and enhancing the presence of material that is useful in tissue repair.
As WebMD states, anxiety that stems from the body's natural way to react to perceived threats can exceed healthy levels. In that case, a victim may suffer loss of sleep, stomach upsets and even panic attacks. This sort of anxiety can hamper one's capacity to execute day-to-day duties. Anyone suffering from overwhelming anxiety should seek professional help.
A human's ability to deal with stress is dependent on a range of factors, as Help Guide explains. Spending time with supportive people at school, in the workplace and in the family can help a great deal.