<prompt> Most severe and persistent symptom for acute mountain sickness is:HeadcheDizzinessDrowsinessCyanosis  <response>: Ans. A: HeadcheHeadaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration.A headache occurring at an altitude above 2,400 metres 8000 feet 76 kPa, combined with any one or more of the following symptoms, may indicate altitude sickness:Lack of appetite, nausea, or vomitingFatigue or weaknessDizziness or light-headednessInsomniaPins and needlesShoness of breath upon exeion 