Final answer:
Marcus may be experiencing altitude sickness, also known as acute mountain sickness (AMS), and should descend to a lower altitude and rest until he feels better. Drinking plenty of fluids and avoiding alcohol and strenuous activity can also help alleviate his symptoms.
Step-by-step explanation:
Marcus is experiencing vomiting and difficulty breathing after skiing. These symptoms may indicate altitude sickness, also known as acute mountain sickness (AMS). AMS occurs when a person ascends to a high altitude too quickly, causing a decrease in oxygen levels and an accumulation of fluid in the lungs.
To alleviate his symptoms, Marcus should descend to a lower altitude and rest until he feels better. He should also drink plenty of fluids to stay hydrated and avoid alcohol and strenuous activity. If his symptoms persist or worsen, he should seek medical attention.