As the liver metabolizes the ethanol, it generates toxic byproducts, most notably acetaldehyde32. The accumulation of these aldehydes midway through the sleep cycle triggers a violent "rebound effect"—a sudden spike in sympathetic nervous system arousal32. This chemical stress response drastically depresses Heart Rate Variability (HRV), elevates resting heart rate, and causes frequent, fragmented micro-awakenings that the individual may not consciously remember but which entirely destroy sleep quality31. Similarly, consuming food immediately before bed forces the gastrointestinal tract into active digestion, diverting massive amounts of blood flow to the splanchnic bed and drastically increasing diet-induced metabolic thermogenesis26. This sudden internal heat production prevents the necessary circadian drop in core body temperature required to sustain deep Slow Wave Sleep24. Establishing a rigid 3-hour fasting and alcohol cutoff guarantees complete gastric emptying and total hepatic ethanol clearance before the head hits the pillow, protecting overnight HRV and hormonal consolidation31.