<prompt> A person unacclimitised develops pulmonary edema in2 - 3 days6 -7 days19 - 21 days2nd - 3rd month  <response>: A small percentage of people who ascend rapidly to high altitudes become acutely sick and can die if not given O2 or rapidly moved to a low altitude. The sickness begins from a few hours up to about 2 days after ascent. Two events frequently occur. Acute cerebral edema and acute pulmonary edema. 