Most common causes of daytime sleepiness

Daytime fatigue, also known as hypersomnia, is an unfortunate fact of life. Occasionally, everyone has a late night, trouble sleeping, or an early alarm that can throw off their routine and leave them feeling sleepy during the day. While it can hurt your productivity and put a damper on your mood, a sporadic sleepy day is nothing to worry about if you know the cause. However, if you’re experiencing chronic hypersomnia and are unsure of what’s causing it, it’s crucial to know the risks associated with this symptom. So, what are the most common causes of daytime sleepiness?

Sleep apnea

Sleep apnea is one of the most common, yet underdiagnosed causes of hypersomnia. As sleep expert Dr. Guy Leschziner explains, “If people are falling asleep during the day, despite not being particularly sleep deprived at night, that is a very common feature of obstructive sleep apnea and is actually rather a worrying one because there are hints that some of the cardiovascular complications of obstructive sleep apnea are associated with being very sleepy during the day.” This daytime tiredness is caused by an inability to sleep due to apnea, frequent micro-awakenings during episodes, and overall reduced quality of sleep.

Poor sleep quality

Even without an underlying condition, chronic poor sleep quality could be to blame for frequent daytime drowsiness. Before seeking a diagnosis, take stock of your sleep habits and environment. Do you use screens or drink caffeine or alcohol before bed? Do you have a dark, quiet environment to sleep in? Are you waking up frequently throughout the night to use the bathroom? All of these things can disrupt your natural circadian rhythms, robbing you of restful sleep.

Mental health conditions

You may not expect the many ways mental health issues can manifest physically, and sleep and well-being are closely linked. Conditions like chronic anxiety and depression have been found to have an impact on more than just mood and can even contribute to daytime fatigue. In fact, one study found that 75% of people with chronic fatigue also have mood or anxiety disorders.

Medication

Certain medications can also be the source of hypersomnia. From prescription drugs to over-the-counter remedies, there is a wide range of medicines that can cause fatigue. Many allergy medications can cause drowsiness, and sleep medications are especially linked to hypersomnia, often leading to a cognitive “hangover” the next morning.

Wondering if sleep apnea is affecting you? Take a few seconds to check out the Dumbo Health Sleep Quiz, and with a few simple questions, you can begin your treatment journey today.

Frequently Asked Questions

Can diet make me sleepy during the day?

Yes. High-carbohydrate meals, eating too much sugar, or large lunches can cause post-meal drowsiness (postprandial somnolence). Balancing meals with protein and fiber can help keep energy levels steady.

Can dehydration cause daytime fatigue?

Yes. Even mild dehydration can lower blood pressure and reduce oxygen delivery to the brain, leaving you feeling sluggish and tired. Aim for steady hydration throughout the day rather than drinking large amounts at once.

Is daytime sleepiness always caused by lack of sleep?

No. Even people who get 7–9 hours of sleep can feel sleepy if they have undiagnosed conditions like hypothyroidism, anemia, or sleep-disordered breathing.

Can certain vitamin deficiencies cause daytime fatigue?

Yes. Deficiencies in vitamin D, B12, or iron are common causes of persistent tiredness. A simple blood test can rule these out and guide treatment.

Is caffeine a solution or a problem?

Caffeine can improve alertness in the short term, but too much, especially after mid-afternoon, can interfere with nighttime sleep, creating a cycle of daytime fatigue.

When should I see a doctor about daytime sleepiness?

If you regularly fall asleep unintentionally (during meetings, conversations, or while driving) or your tiredness is affecting daily life, you should seek medical advice. Persistent sleepiness can signal an underlying condition that needs treatment.

Wondering if sleep apnea is affecting you? Take a few seconds to check out the Dumbo Health Sleep Quiz, and with a few simple questions, you can begin your treatment journey today.