Cortisol and nervous system is regulating :) alcohol gives you a boost in dopamine and GABA followed by a crash. After you quit, your body needs to re-balance without this frequent boost and crash that you get from drinking. Alcohol also 'numbs' anxiety, stress etc temporarily and even interrupts REM sleep. Your body was likely in survival mode and focussed on functioning at the time, and now it is working to heal and regulate :) that's my guess anyways!