“Why does bronchitis make you so tired?”

Any infection will cause fatigue.

Hi!
Bronchitis is inflammation of the Airways that carry air to and from the lungs - Overwhelming inflammation drains your immune system and makes us feel tired as the body is fighting the source of infection. So any compromised baseline health (anemia/vitamin deficiencies etc) can get fatigued standing up to the challenge. It will serve you well to check your baseline health to ensure you are fine otherwise and not nutritionally or metabolically compromised. Having an annual physical exam helps you keep tabs on your baseline health. Eating a nutritious well balanced diet and keeping yourself hydrated well also helps during sickness and help avoid tiredness.

Bronchitis is an active, though localized infection, in the bronchial tubes that causes inflammation and energy expenditure to fight it. That alone can contribute to fatigue. Sometimes bronchitis impairs the free flowing movement of air into and out of the lungs, another reason that can contribute to fatigue. Bronchitis is also a clinical diagnosis and often there is no chest xray to confirm the presence or absence of pneumonia. The presence of pneumonia makes all of the above worse. Finally, with bronchitis or pneumonia, you are typically coughing and expending energy which can also contribute to feelings of fatigue.