Is diarrhea part of altitude sickness?

Unusual but can: Could more likeley be something else. I would look for other causes. First on the list what did you eat recently.

Altitude sickness: Nausea and vomiting occurs in many with altitude sickness. Diarrhea is less common and has not been statistically confirmed as increased, though it is reported as is loose stool and may be related to other hygiene factors,as well. https://www.ncbi.nlm.nih.gov/pubmed/17542291 http://www.nepaltrekkinginfo.com/nepal/trekking/altitude_sickness.html