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Source: https://outdoors.stackexchange.com/q/16183
License name: CC BY-SA 3.0
License URL: https://creativecommons.org/licenses/by-sa/3.0/

<p>Recently I did a trek in the Himalayan region and one of the group members was affected by what we believed was AMS at around 4600m. 
We had to evacuate the person from there and get to around 4100m before she stabilized. </p>

<p>On review of the situation we found the following:</p>

<ul>
<li>She did not have any headache or nausea. She just fainted. Which pointed towards lack of oxygen supply to her brain (subsequently she fainted around 5-6 times while we were bringing her down). </li>
<li>The person concerned was on Diamox (should have helped her acclimatize, but I realize that this is not a guarantee). </li>
<li>She was well hydrated (she was drinking around 4L of water per day).</li>
<li>She did exert herself a bit more than required before AMS hit her (she was breathless as well, which is a symptom of AMS). There were no symptoms of headache or any nausea before that (or even after).</li>
<li>Her oxygen reading was around 85% and her HR was registered at 140+ around the time she fainted.</li>
<li>We had to administer Dexamethasone steroid to boost her lungs up and we saw an improvement in her condition in about 45min.</li>
</ul>

<p>So my question is, can overexertion lead to AMS? Would it act as a possible factor in increasing the chances of a person being affected by AMS? </p>

<p><em>PS:</em> I had a doubt if it was AMS in the first place, but since  there's a possibility of lack of oxygen causing her to faint, I'm assuming it was AMS. </p>

<p><em>Based on one of the answers given by @wills, I'm adding further clarifications:</em> </p>

<p>The person concerned did mention that she witnessed the 'darkness in front of eyes' before fainting, so I'm ruling out weakness as the reason. Also, this continued to happen some 5-6 times in the next 1 hour or so. </p>