Yeah, that reflex is definitely common. Appetite suppression is, I think, associated with hypoxia. But at least initially, your BMR increases. So your body is hungrier, despite you not feeling it. You're actually in pretty serious calorie deficit.
Abrupt exposure to elevations greater than 10,000 ft (3,050 m) is frequently associated with symptoms of altitude illness. Altitude illness is a combination of symptoms, including headaches, anorexia, nausea, vomiting, and malaise. The combined effect of these symptoms is usually a profound depression of appetite and reduction of food intake, just at the time when the climber needs energy the most. Climbers that anticipate the consequences of altitude-impaired appetite may at least minimize the secondary consequences of the cachexia of altitude: reduced energy intake, depleted muscle glycogen stores, negative nitrogen balances, and loss of critical lean body mass.
Gradual acclimatization to progressively higher altitude exposure is the best preventive medicine for high-altitude sickness. Unfortunately, it is not always practical or possible to delay ascent to altitude. Rescue workers frequently must travel abruptly to high altitudes to perform critical tasks. Prior acclimatization is not always possible. Abrupt transportation from sea level to high altitude may be accompanied by debilitating altitude sickness symptoms, including altered mood, appetite, and performance. These uncomfortable symptoms usually increase in intensity for periods of up to 48 hours after altitude exposure and then gradually lessen. Unfortunately, it is usually during the first 48 hours at altitude that critical work must be accomplished. The strenuous activities associated with work or recreation at altitude, plus an initial increase in resting metabolic rate and the lack of adequate food intakes almost invariably result in an initially negative energy balance. Altitude illness can limit volitional activity, but energy expenditures of experienced and motivated climbers who are acclimatized can be quite high, depending upon the activity level achievable under hypoxic conditions.