Altitude sickness is very common among trekkers during himalayan treks, it is wise to consult your doctor for the right medication before your trip. Drinking lots of water can also help stabilize the body along with resting at regular intervals. The best rate of acclimatization is to gain no more than 300m (1000 feet) per a day. If you increase this rate you will be much more susceptible to Elevation Sickness. Getting adequate sleep also can help avoid this.