A short burst like this can happen for several reasons—some harmless, some that need checking: Common & often treatable causes • Anxiety or panic attacks during sleep Sudden adrenaline release → racing heart, feeling startled awake. • Sleep apnea (very common and under-diagnosed) Breathing pauses → oxygen drops → heart rate suddenly shoots up. • Acid reflux (GERD) Especially when lying flat; can stimulate the vagus nerve and heart. • Dehydration or electrolyte imbalance Low potassium/magnesium can trigger palpitations. • Caffeine, alcohol, nicotine (even hours earlier) • Poor sleep schedule / stress overload Medical causes that MUST be ruled out • Arrhythmias (SVT, atrial tachycardia, AF episodes) • Thyroid issues (hyperthyroidism) • Low blood sugar at night • Anemia • High sympathetic nervous system activity A resting sleeping heart rate over 100 bpm, even briefly, is not considered normal and deserves evaluation.