Why do climbers at high altitude experience shortness of breath, dizziness, nausea and tinnitus?

Low oxygen pressure in the air at high altitude causes hypoxia – oxygen starvation with the symptoms described, this is the so-called mountain sickness; at the same time, there is a need to breathe more often, the concentration of carbon dioxide in the blood decreases, the blood becomes alkalized, breathing may be interrupted, and loss of consciousness is possible. Climbers use oxygen machines, ascorbic or citric acid.