Yes, you cannot do Everest Base Camp Trek without proper acclimatization. At least, 2 days of acclimatization is must beforehand you go to step your foot at Everest Base Camp. We will take first day acclimatization at Namche and the second day acclimatization at Dingboche in Everest Base Camp Trek. You are prone to the risk of altitude sickness if you do not get proper acclimatization. Do not ascend quickly in rush while doing your Everest Base Camp Trek. Your body needs acclimatization.