A DAILY DISCOVERY / Sleep and light
Why do waking and dreaming trigger an uptick in heart activity?
As you move through different sleep phases, your cardiovascular system shifts gears. During deep non-REM rest, your heart rate and blood pressure drop as the parasympathetic system dominates. However, during REM sleep and the process of waking up, your sympathetic nervous system kicks in, elevating blood pressure and heart rate back to typical waking levels.
Why it happens
The body switches autonomic control depending on the sleep phase. During non-REM sleep, the parasympathetic system leads, allowing the heart to rest and blood pressure to fall. When you enter REM sleep or start to wake, your sympathetic nervous system activates. This activation raises heart rate and blood pressure toward daytime baselines. Research notes that a sharp rise in blood pressure and heart rate upon waking is linked to events like chest pain (angina) and heart attacks, particularly if sleep is deficient or fragmented.
Something to notice
Notice if your mornings feel rushed; taking a calm, unhurried moment to sit up in bed allows your body to smoothly transition its cardiovascular rhythms.
Keep the context
These autonomic shifts are a standard part of human physiology, but chronic poor sleep or frequent awakenings can increase long-term risks for high blood pressure and coronary heart disease.
Seek emergency medical care immediately if you experience chest pain, pressure, or symptoms of a heart attack upon waking.
Sources and limits
Sleep and light
Source retrieved 2026-10-25
Written with AI assistance and checked automatically against the linked source material. This is not a clinician-reviewed article or a diagnosis. Source retrieval does not establish clinical review. Our editorial approach.