Monophasic sleep is a sleep pattern in which all of a person’s daily sleep is consolidated into a single, uninterrupted block, typically occurring at night. It is the most common sleep pattern in industrialized societies and is considered the cultural norm in many parts of the world, where a single nighttime sleep period of 7 to 9 hours is the standard. The prevalence of monophasic sleep in modern Western societies is largely shaped by social, cultural, and economic factors — particularly the structure of the working day, which typically requires alertness during daylight hours and allows for sleep only at night. The widespread use of artificial lighting has also played a role in consolidating sleep into a single nighttime period. From a biological perspective, however, some researchers argue that monophasic sleep may not be the most natural sleep pattern for humans. Historical evidence and studies of pre-industrial societies suggest that biphasic sleep — a longer nighttime sleep combined with a midday rest or afternoon nap (the “siesta”) — may be more aligned with our circadian biology. Many people experience a natural dip in alertness in the early afternoon that may reflect an innate drive for a brief midday rest. For most adults in modern societies, monophasic sleep works well when the timing and duration of the single sleep period are adequate and consistent. Going to bed and waking at the same time each day, within an appropriate schedule that allows for 7 to 9 hours of sleep, is generally sufficient to meet the body’s sleep needs. If a person consistently struggles to achieve restorative sleep within a monophasic pattern, exploring supplementary short naps or consulting a sleep specialist may be beneficial.