Why would a persons oxygen level fall and heart rate increase?

A person's oxygen level may fall due to various factors, such as respiratory issues (like Asthma or pneumonia), reduced lung function, or high altitudes. When oxygen levels decrease, the body responds by increasing heart rate to pump more blood and deliver oxygen to vital organs and tissues. This compensatory mechanism aims to maintain adequate oxygenation despite the lower levels available. Additionally, anxiety or stress can also elevate heart rate while contributing to feelings of breathlessness, further impacting oxygen saturation.