The altitude is a strange phenomenon. Everyone is affected - for me days 3-5 are tough - no sleep, short of breath, dehydration, digestive issues. Coca tea is the panacea - it really is a cure-all!
After a few days you are fine. Digestive issues remain - there are very few fat people here - overeating is uncomfortable.
You do realise the effects when you get down to sea level if you get there quickly. A flight sort of screws it all up.
Thank you for the comments - much appreciated