Looking into this after class today. Are you on this diet? And for the caffeine and L-theanine, I thought the latter was a relaxant. Intersting mix.You could try eating a low carb/low glycemic index dinner. Your body's insulin level spiking after you eat can lead to you feeling more sleepy and foggy-headed.
I dabble with keto and intermittent fasting, but I'm not strict about it. Low carb is handy for losing weight because it decreases appetite. I find it gives me a more steady energy. No energetic highs, but no crashes either. The important thing related to energy is that sugar (and high glycemic index foods that quickly turn into sugar) cause your blood glucose to go high, then low. This will make you feel more tired. Cognition also correlates with glucose levels, so eating a carb-heavy dinner before class is probably not optimal, due to the drop in blood glucose level. L-theanine is a relaxant, but it creates a nice focus when in the right balance with caffeine. I like the way it makes me feel-- it's like I can calmly direct my attention where I want it, or just relax. Caffeine by itself is more energetic, but way more intense. I won't claim caffeine+theanine is a nootropic, but some people think it is.