Ever Woken Up Moody After an Evening Sleep? Here’s Why - Dr Afeefa M Hakeem

Almost everyone has experienced it at least once: you lie down for a short evening sleep, thinking it will refresh you, but you wake up feeling oddly irritable, heavy-headed, or emotionally off balance.

Patients often describe it as “uneasiness,” “low mood for no reason,” or simply “not feeling like myself.” As someone working in emergency medicine, I’ve heard this repeatedly in the emergency room, during casual conversations with colleagues, and even noticed it personally on days when duties force irregular sleep. What seems like a small everyday complaint actually has a strong biological explanation.

Human emotions are not random throughout the day. They are closely tied to our internal biological clock, the circadian rhythm,m which regulates not only sleep and wakefulness, but also hormones, body temperature, alertness, and mood. A study by Emens and colleagues clearly demonstrated that mood follows a circadian pattern independent of sleep duration.

Their research showed that negative emotions naturally rise during the biological night, while positive emotions peak during the biological day. This means that even if you sleep for an adequate number of hours, sleeping at a time when your brain is not biologically prepared for restorative sleep, such as early evening can leave emotional circuits poorly reset, resulting in irritability or emotional dullness on waking.

Earlier experimental work by Boivin and colleagues further clarified this relationship. They found that mood deterioration was more strongly linked to circadian misalignment than to sleep deprivation itself. In other words, sleeping at the wrong time can feel worse than sleeping too little. This finding resonates strongly in clinical settings. In emergency departments, many of us try to “sleep early” before night duties, only to wake up feeling disoriented, emotionally flat, or inexplicably low despite technically having slept enough.

More recent evidence supports this observation. A study published in Scientific Reports examining simulated shift work found that circadian misalignment alone significantly increased mood vulnerability even in healthy individuals.

Participants developed irritability and negative mood states simply because their sleep timing conflicted with their internal clock. Research on chronotypes also explains why not everyone experiences evening sleep the same way. Randler and colleagues showed that morning-type individuals are especially sensitive to poorly timed sleep, which may explain why some people strongly dislike evening naps while others tolerate them better.

There is also an important difference between a short, well-timed nap and prolonged evening sleep. Tietzel and Lack demonstrated that brief naps taken earlier in the afternoon improved mood and alertness without disturbing nighttime sleep. In contrast, longer or later naps interfered with sleep pressure and circadian rhythm, often leading to grogginess and emotional discomfort after waking. Clinically, this matches what we observe: a short afternoon nap can be refreshing, but sleeping close to sunset often feels unsettling rather than restorative.

What is fascinating is that long before modern neuroscience described circadian rhythms, many cultures instinctively discouraged sleeping after sunset. Traditional Hindu and Ayurvedic teachings describe sunset as a transitional period meant for prayer, reflection, and light activity rather than sleep, associating evening sleep with lethargy.

Islamic teachings also mention discouragement of sleep around sunset, and similar beliefs appear across ancient civilisations. While these traditions were not scientific in nature, they likely emerged from generations of observing how human energy and mood fluctuate with natural light. Modern sleep science now offers a biological explanation for what ancient societies intuitively understood.

In today’s world, where artificial lighting, screen exposure, and demanding schedules blur natural rhythms, evening sleep is sometimes unavoidable. The issue is not that evening sleep is “bad,” but that frequent or prolonged sleep before the body enters its biological night can disrupt emotional regulation. In emergency medicine, where circadian disruption is almost unavoidable, we see firsthand how mood, patience, and emotional resilience suffer more from mistimed sleep than from mild sleep deprivation itself.

So if you find yourself feeling low or irritable after an evening's sleep, it is not weakness, laziness, or imagination. It is your biology speaking. Aligning sleep timing with your natural rhythm,  even imperfectly,  can make a remarkable difference to emotional well-being. Perhaps this is one of those rare spaces where ancient wisdom and modern science quietly meet, reminding us that listening to our body’s timing may be just as important as listening to our body’s need for rest.

Disclaimer: The views expressed in this article are of the author and not of Health Dialogues. The Editorial/Content team of Health Dialogues has not contributed to the writing/editing/packaging of this article.