During an allergic reaction, the body releases proinflammatory cytokines to neutralize the foreign bodies, and these proinflammatory cytokines cause fatigue, according to Health Guide Info. The cytokines react with the central nervous system and cause a variety of cells, like leukocytes, to secrete a hormone-like substance known as interleukin-1-beta that causes fatigue. Fatigue encourages the affected individual to rest more, so that the body has more energy to deal with the invasion of the foreign bodies.
Those who struggle with allergic rhinitis have a high chance of dealing with insomnia as well, which can cause them to feel more tired than usual. In addition, most allergy medications induce drowsiness.