If you acclimate properly, altitude sickness is not an issue. Above 3000m, your sleeping elevation gain should not increase over 300 to 500 m per night. There are many villages and tea house along this trek so you can easily ascend only 300 to 500 m per night. Sleeping elevation is so important because you spend so much time sleeping. Every individual is different and the same person can experience different reactions to altitude on different trips. Above 3000m, first try ascending only 300 m per night. If you handle that well, then you could try pushing it to 500 m per night, but don’t go above that! There is a delay of 7 to 12 hours after arriving at altitude before you start to experience altitude related symptoms. You can arrive at an elevation and feel great, but then you could wake up in the middle of the night with severe altitude related issues. Acclimate properly. You can take Diamox (Acetazolamide) to help with acclimating. Consult a physician to determine if you should take it. People that have certain medical conditions (like liver or kidney disease, allergic to sulfur drugs, etc.). There are other people that shouldn’t take this medication so consult with your doctor.