 The higher we go up in elevation, the less oxygen there is for our body to consume and so it becomes difficult for the human body to to deal with these changes in elevation. At this elevation, the human body starts experiencing symptoms of high altitude sickness. Usually it's headaches, dizziness, nausea, sometimes sleepiness and the most severe form would be high altitude cerebral edema and this is when the brain swells in fluids from being at high altitude. These are some side effects that you should be aware of.