You might have read about Robbie Savage the ex professional soccer player and Welsh international being struck down with serious altitude problems at 12,000 feet on Kilimanjaro. This is similar height above Namche Bazaar on the Everest Base Camp Trek or on day 3 of the Lemosho route up Kilimanjaro. Ignorance to the risk of lack of oxygen to common. You need to educate yourself to the risk of going into a low oxygen environment. Altitude sickness is real.
I am not sure what route Robbie Savage was climbing on or what rate of ascent their team were on, but once you go above 9,000 feet you should ascend no faster than 650m/ 2,000 ft per day. Ideally you want 2/3 night spend around 9,000 / 11,000 feet before ascending further. Climbing high and sleeping low and keeping well hydrated 4 /6 liters per day is vital. You can also take Asprin or Disprin in your water daily to thin out the blood.
The most important thing to remember is take more days climbing on Kilimanjaro. It will cost more for each extra day you spend in Kilimanjaro national park. It is not worth getting sick and having to turn around, that is a waste of your time, preparation and money. Be smart and be safe. Take more time and acclimatize to the low oxygen levels correctly. Anyone trying to sell you a 4,5 or even 6 day trip are risking your life and taking unnecessary risks. We recommend taking 7 or 8 days to climb Kilimanjaro. It is a waist of your money to try and climb Kilimanjaro in 5 days, feel like crap and not enjoy the challenge. Take the extra days, acclimatize properly and enjoy your climb.
You want to be there when the sun rises on your summit night. Standing on the summit of Africa’s highest mountain and enjoying your achievement. Not in a hospital, or struggling to get back down off Kilimanjaro.