Students usually end up sacrificing something; it's a rare feat that every single task and goal gets accomplished. Something has to go. Effort is spent more on certain activities than others. For example, occasionally studying takes precedence over sleep and work somehow decreases the likelihood of eating a proper meal. It happens, occasionally.
However, it may be worth the effort to catch those extra Z's and not skip meals.
In an article by the National Institution of Mental Health, a lack of sleep can result in a decrease in performance, concentration and even reaction time. Eight hours of sleep is the magic number suggested for adults (education.com).
As far as skipping meals go, the side effects outweigh any positives. Not only does skipping meals actually decrease the metabolic rate, but it also zaps whatever energy remains in our bodies and can also impair our concentration. That's why we hear that eating a good breakfast and getting a good night's sleep is good before a test day. Our bodies should be functioning at their best, physically, so we can perform at our best, mentally.
Another essential to a high energy level is water. Dehydration is a common factor of fatigue. Drinking enough water each day helps a lot of bodily functions. It's meant to be. A quick tip: if you are drinking only filtered water, make sure to supplement with an electrolyte drink, as bottled water is stripped of all minerals.
Food. Try to eat as much real food as possible. It's hard, but worth it if you want your bod to perform at its best. The less that has been done to the food, the better. When food is processed, the nutritious parts are eliminated, and artificial additives take their place. There are tons of places to learn how to prepare the easiest, yummiest nutritious foods (and still be able to afford rent). The answer is almost guaranteed to be in a blog on Pinterest, somewhere.
Higher energy in the body also relieves stress, and can increase the level of happiness within. If you think you wouldn't mind more energy or happiness in every day, try and make it yourself.