It is hard to accept that we need fuel like plants need the sun. Our cells use chemical energy to operate. The energy in the glucose is used catalythically to create new bindings between the atoms of molecules. Molecules that will operate our complicated inner machinery. Glucose also drives the operation of the cell membrane of nerve cells to conduct electrical charge. The list goes from muscles activity to chaining fat for energy storage to unchaining fat to release body heat.
The brain alone will consume 4g of glucose per hour. Add heart and other muscles, body heat and billions of bacteria in your gut and you will come to impressive figures for our hourly glucose consumption. This is why 48 mg/dl will get consumed very quickly. If your finger is at 48 mg/dl your brain will be lower because the consumption rate is very high in the brain. This is why numbers below 70 mg/dl will start to impact brain functionality. Especially the higher functions like our intellect can be slowed down. This definitely starts below 60 like two devils sitting on your shoulder: test and treat the low VS do what you really want to do. With time I have developed habbits to give the low the highest priority first. This goes so far to rest for 10 minutes to help the glucose to be absorbed. It pays out because I can continue sooner with my planned activities. It is a form of patience with yourself or even humbleness.