I arrived in Cusco early yesterday (6.30am) after flying from Lima (and before that, Buenos Aires). I felt pretty light headed within an hour of landing and we rested at our hotel as advised. By 2pm I was in agony, a splitting headache, nausea (which led to vomiting), restlessness, and feeling very off balance. We called a doctor who tested my oxygen levels and they were low at 82%. I got admitted to the oxygen clinic and got put on oxygen and an IV for 18 hrs. Staff were fantastic and checked me regularly. I was diagnosed with acute altitude sickness. I wanted to post this as I am a healthy 29 year old and did not think I would get such severe symptoms so quickly. As I have been travelling for 4 months and only decided to come to cusco recently, I was not able to see a doctor before coming, but I would urge travellers to read up and seek medical advise prior to coming here. I am feeling better now and am crossing everything that I will be ok to visit Machu Picchu tomorrow.