I'm doing my first marathon (VLM) in April and have eventually found an energy gel (High 5) that doesn't engage my "gag reflex". According to the High 5 literature, one sachet should be taken every 20 mins (for a 3.30 marathon schedule). I tried this yesterday on my half marathon route and felt awful ! I know everyone is different, but i don't want to run out of energy during the race. Any tips/advice?