From the 100 Facts for 100 years of Machu Picchu- Fact #11

By Catharine Hamm Los Angeles Times travel editor

11. Among the problems AMS can cause (if you're coming from sea-level California, be aware of this): headaches, shortness of breath, fatigue and/or nausea or vomiting. Consult a doctor before you go if you think you may have a problem. Symptoms usually disappear in four days, but in some cases, AMS may be fatal.

The best remedy for altitude sickness is to go to a lower elevation.  Cusco is at 11,200 feet elevation while the Sacred Valley is at a lower elevation.  Ollantaytambo for example is at 9,160 feet above sea level and Machu Picchu is at 7,970 foot elevation.  For many travelers spending the first night in Cusco then descending to the Sacred Valley and spending the night there before heading to Machu Picchu will help make the trip more enjoyable.