This is more of a psychiatry question then a biochemistry question.
Alcohol is a GABA agonist; GABA is a inhibitory neurotransmitter so alcohol use causes inhibition of certain brain functions.
The constant agonism of GABA results in ↓ expression of the GABA receptor and a ↑ expression in the glutamate (excitatory) receptor.
W/d alcohol causes over-excitation of glutamate receptors → activation of the SNS → anxiety, agitation, hallucinations, seizures, and ↑ BP and ↑ HR (classically manifesting as delirium tremens).
I'm not sure why bradycardia would occur. Tachycardia is part of the classic presentation of alcohol w/d.
There is a biochemistry tie in to alcoholism; alcoholism causes a B1 deficiency which results in inflammation/necrosis of the mammillary bodies, thalamus, and hippocampus. This presents as Wernicke encephalopathy, a triad of opthalamoplegia, encephalopathy, ataxia. Repeat Wernicke encephalopathy episodes leads to Korsakoff syndrome, which presents as irreversible, permanent amnesia, memory impairment, and confabulations (making up stuff).