Symptoms: drowsiness, dizziness, fainting, severe prolonged headaches, extreme thirst, sleeplessness, appetite loss, weakness, nausea, vomiting, heart palpitations, pounding pulse, congested lungs, difficulty breathing and coughing can all be symptoms of altitude sickness. Some of these conditions can be life-threatening. Being in excellent physical condition has no bearing on one’s ability to acclimate to higher altitudes.