Yes. The caffeine in coffee gives you an energy boost, but it also blocks your adenosine receptors. Adenosine is what helps regulate your sleep-wake cycle. When the coffee wears off, the receptors are flooded with adenosine which can make you feel tired. Putting too much sugar in your coffee can also cause a blood sugar spike that is followed by a crash. More than 400 mg of caffeine in a day (4-5 cups of coffee) can interfere with your sleep cycle which will leave you feeling tired.