Can drowsiness cause tachycardia?

Drowsiness Does Not Cause Tachycardia—The Opposite Occurs

No, people do not get tachycardia when they feel sleepy; drowsiness and sleep are associated with bradycardia (slower heart rate), not tachycardia. This is a fundamental principle of autonomic cardiovascular regulation during sleep states.

Physiological Heart Rate Changes During Sleep and Drowsiness

• Heart rate decreases progressively as sleep deepens, with the lowest heart rates occurring during slow-wave (deep) sleep due to increased parasympathetic (vagal) tone and reduced sympathetic activity 1, 2.

• Sleep processes exert the predominant influence on 24-hour heart rate profiles, with heart rate variations being mainly sleep-stage dependent rather than circadian-driven 2.

• Bradyarrhythmias are the characteristic rhythm disturbances during sleep, including exaggerated sinus arrhythmias, transient AV block, and profound sinus bradycardia—not tachycardia 1.

• Nocturnal bradycardia is a normal physiological finding, with rates commonly dropping below 40 beats per minute in healthy individuals, particularly young people and conditioned athletes, without any pathological significance 3.

When Tachycardia Occurs With Drowsiness: Red Flags

If a patient reports tachycardia when feeling drowsy, this represents a pathological state requiring investigation:

• Sleep apnea causes a stereotypical pattern of bradycardia during apneic episodes followed by tachycardia upon arousal due to hypoxia-induced sympathetic surge—this is not drowsiness causing tachycardia, but rather interrupted sleep with hypoxic stress 3.

• The prevalence of profound nocturnal bradycardia in sleep apnea ranges from 7.2% to 40%, with second- or third-degree AV block occurring in 1.3% to 13.3% of cases 3.

• Postural orthostatic tachycardia syndrome (POTS) presents with marked heart rate increases (>30 bpm or >120 bpm) upon standing in young women with orthostatic intolerance, but this is triggered by postural change, not drowsiness itself 3.

Clinical Pitfalls to Avoid

• Do not confuse the tachycardia that occurs during transitions from deep sleep to lighter sleep or awakening with drowsiness-induced tachycardia—these abrupt heart rate increases occur during arousal from sleep, not during the process of becoming drowsy 2.

• Drowsiness as a symptom accompanying tachycardia suggests the tachycardia is causing the drowsiness (via reduced cerebral perfusion), not the reverse—this occurs when tachyarrhythmias compromise cardiac output 3.

• Drug-induced drowsiness with tachycardia indicates anticholinergic or sympathomimetic toxicity, as seen with pimozide or haloperidol overdose, where drowsiness and tachycardia are parallel toxic effects, not causally related 4, 5.

The Correct Physiological Sequence

The normal cardiovascular response to drowsiness and sleep onset is:

1. Progressive decrease in heart rate as parasympathetic tone increases 1
2. Reduction in blood pressure 1
3. Decreased sympathetic nerve activity 6
4. Lowest heart rate variability during slow-wave sleep 2

If tachycardia is present when a patient feels drowsy, investigate for:

• Underlying physiologic stressors (fever, dehydration, anemia, hypoxemia) causing both symptoms independently 3, 7
• Sleep-disordered breathing with hypoxic arousals 3
• Drug effects or toxicity 7, 8
• Primary cardiac arrhythmias causing reduced cerebral perfusion and secondary drowsiness 3