It's interesting you mention sugar. There's also a biological component here--diet plays a huge role in how your brain works. For example, on a ketogenic diet

It's interesting you mention sugar. There's also a biological component here--diet plays a huge role in how your brain works. For example, on a ketogenic diet (no sugar and limited carbs) your brain produces ketones and many people report far less lethargy. Sugar helps in the short-term, but if you get past the keto-flu, you no longer become glycogen dependent. Long-term ketogenic diets are now finally being studied, with many people reporting tremendous success. Psychiatrists love giving you sugar and drugs though. Any drugs, any sugar!