High altitude can bring even experienced mountain climbers have difficulty in hiking the mount Rinjani. You should take it easy from the beginning of the hiking. Though it may feel easy in the first hour, you need to save your energy for the next hiking challenge. This applies the same for the Mount Rinjani summit hiking in the following day, just keep it slow and steady and you should be fine and able to reach the summit.
Some people are affected more than others by high altitude sickness. High altitude sickness tends to take effect on the Mt Rinjani hiking in last couple of kilometres to the Mount Rinjani summit. People may experience an elevated heart rate, even when resting, and a feeling of breathlessness near the Rinjani summit. Mostly a slight headache will be their only symptom which easier to manage by taking paracetamol and plenty of water.
However, others can be overcome by nausea symptom. If you are not hiking Rinjani at a slow, steady pace, there is little chance that you can avoid high altitude sickness. The only remedy for high altitude sickness is to return to lower altitude.
Of course if you prepare your stamina well then most likely you will be able to overcome this high altitude sickness.