5. Fatigue
As the air sacs are responsible for extracting oxygen from the air and helping it to saturate the blood, it should come as no surprise that an infection affecting this part of the body will make it more difficult for you to breathe.
This may not necessarily be felt as breathlessness (though it often can be) but will make it more difficult for the muscle and brain to get the necessary energy that they need. As such, this can cause tiredness and fatigue and make your usual activities more difficult.
Similarly, it is also common for pneumonia to cause patients to feel aches and pains in their muscles, which is caused by the same process. Simple tasks may become difficult and painful.