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The alarm rings, you awaken, and you are still drowsy: why? Being sleepy in the morning does not make any sense; after all, you have just been asleep for the past eight hours. Shouldn’t you wake up refreshed, aroused, and attentive? No, and there are a series of ways to explain why.

The Neurobiological Answer

During the previous few hours before waking in the morning, you spent most of your time in REM sleep, dreaming. (If you would like to read more about the basics of sleep, see my book, The Brain: What Everyone Needs To Know.) Your brain was very active during dreaming and quickly consumed large quantities of the energy molecule ATP. The “A” in ATP stands for adenosine. The production and release of adenosine in your brain are linked to metabolic activity while you are sleeping.

There is a direct correlation between increasing levels of adenosine in your brain and increasing levels of drowsiness. Why? Adenosine is a neurotransmitter that inhibits (i.e., turns off) the activity of neurons responsible for making you aroused and attentive. You wake up drowsy because of the adenosine debris that collected within your brain while you were dreaming.

What should you do about the negative effects of adenosine?

Have a cup of coffee or tea. Numerous studies have shown that adenosine worsens cognitive decline, while caffeine, by blocking the action of adenosine, improved cognitive ability. In addition, caffeine from coffee or tea reversed the level of oxidative stress and inflammation that is caused by adenosine.

Did You Go to Bed Late Last Night?

People who prefer to stay out late (evening types), get up later, and perform best, both mentally and physically, in the late afternoon or evening. Evening-type individuals were significantly more likely to suffer from poor sleep quality, daytime dysfunction, and sleep-related anxiety as compared with morning-type individuals. Even more disconcerting is that late bedtime is associated with decreased hippocampal volume in young, healthy subjects. Shrinkage of the hippocampus has been associated with impaired learning and memory abilities.

What, and When, Did You Eat Last Night?

What you eat before bedtime also might improve your chances of getting a good night’s sleep. Eating something sweet might help induce drowsiness. A recent study investigated the interval between the last meal and bedtime and its effects on sleep.

Their results showed that for every hour decrease in the interval between the last meal and sleep onset, there was an increase of 23 minutes in sleep duration. Elevated blood sugar levels have been shown to increase the activity of neurons that promote sleep. These neurons live in a region of the brain that lacks a blood–brain barrier; thus, when they sense the presence of sugar in the blood, they make you feel drowsy.

This might explain why we feel like taking a nap after eating a large meal. It's just one more bit of evidence demonstrating your brain’s significant requirement for sugar to maintain normal function. A peanut butter and jelly sandwich provides some carbohydrates and proteins that will enhance the uptake of tryptophan into the brain.

Who Did You Sleep With Last Night?

Couples sleeping in pairs were investigated for sleep quality, that is, for the correct balance of non-REM and REM, as well as their own subjective view of how they slept. For women, sharing a bed with a man had a negative effect on sleep quality.

However, having sex prior to sleeping mitigated the women’s negative subjective report, without changing the objective results, that is, their balance of non-REM and REM was still abnormal. In contrast, the sleep efficiency of the men was not reduced by the presence of a female partner, regardless of whether they had sexual contact.

In contrast to the women, the men’s subjective assessments of sleep quality were lower when sleeping alone. Thus, men benefit from sleeping with women; women do not benefit from sleeping with men unless sexual contact precedes sleep—and then their sleep still suffers for doing so. Studies show that these negative effects on women are mitigated by the closeness of the relationship and involve the activation of oxytocin neurons.