All visitors must ensure they are physically fit before visiting Ladakh and Lahaul and Spiti. The high altitude environment is demanding. People with heart or lung disease must consult their doctor before planning a trip. Acclimatization is mandatory for visitors traveling by air. It is important to take complete rest for the first 24 hours after arrival and as much rest as possible for the next 12 hours. People traveling to altitudes above 10,000 feet (2700 m) are likely to suffer from acute mountain sickness. The most common symptoms are disturbed sleep, loss of appetite, nausea, coughing, irregular breathing, breathlessness, lack of concentration. In its more serious form, acute mountain sickness can be life threatening and so needs immediate medical attention.