The oxygen concentration in the air decreases as the altitude increases. Due to the relatively low elevation profile, the likelihood of altitude sickness during the Upper Mustang Jeep ride is very low. However, be careful when you start showing signs, as it exceeds the 3500 m threshold.
Headache, dizziness, difficulty sleeping, nausea, loss of appetite, rapid pulse, and shortness of breath are all symptoms of altitude sickness. If you have any of these symptoms, please immediately contact your guide. Then, take a break, drink plenty of water, and return to lower altitudes if the situation seems worse.
So, make sure you have health insurance from a reputable company valid in Nepal for this trip.