3-Fatigue
Oxygen is essential to create energy from glucose and other energy sources. Similar to what happens in the lungs, there’s a place in the cell where oxygen is received, and the respiration process creates molecules called ATP. These ATP molecules speed up metabolic process and help us keep moving and thinking properly. A shortage of oxygen leads to an energy deficiency and both physical and mental tiredness that is maintained over a very long period of time. In most cases, the severity of this symptom increases as the circulating levels of hemoglobin are reduced.