I was watching a presentation a few days ago and realised that not only did the audience look sleepy after lunch, so did the presenter. I noticed that during the luch break the presenter was available for the people in the room for the whole of the break. Available to answer questions and discuss her products and generally have friendly conversaitions.
I observed that after the break the flow of the presentation and the energy that had been present in the morning session, was lacking.
I believe that as a presenter you must take care of yourself so you can be present for your audience. Find the way that you best refresh yourself and energise yourself so your energy levels do not fail you at a time when you are required to give your all to your audience.
There are many ways to charge your batteries. You may already know what works for you. Is it getting some fresh air, drinking plenty of water, taking a short walk to clear your mind and plan your next session. It may be sitting quietly on your own or chatting to your support person and getting some feedback on how the session was tracking so far, and deciding if you have to tweak anythink to come.
Whatever works for you, plan to include this into your day and stick to the plan.
Remember to eat well, drint plenty of water and ensure you have enough sleep prior to the event. That way you will keep healthy and your energy levels will be up to give your best presentations every time.