alcohol is on a very general level a depressant of the central nervous
system. the more alcohol  you consume within a given timeframe the
higher your blood level of alcohol, hence a higher degree of central
nervous system depression. the morning after the alcohol is waring off
and you are experience a type of post-depression excitatory rebound.
have you ever heard the phrase for every action there is equal but
opposite reaction. the human body is not an exception. your own bodys
nervous system is complex web of excitatory and inhibitory process that
more or less keep everything in check. when you consume enough of a cns
depressant such as alcohol or other drugs such as narcotics or
sedatives your body responds by inhibiting the activity of inhibitory
functions in the cns in attempt to equalize things as much as it can.
the next morning(providied you have not continued to drink anymore) the
alcohol levels have dropped off sharply and is having very little or no
depressant effect on your nervous system at this point. however, that
decrease in inhibitory function in your nervous system as result of
your previous nights alcohol consumption is still in effect. although
once consumed the alcohol goes to work very quickly your bodily
responses to the alcohol are more slow and subtle. so as i just said
you still have this decrease in inhibition in your nervous system which
will leave some the excitatory processes(adrenaline and noradrenale)
more active and with less inhibitory competition. so you cns system is
in somewhat excited state with your body having elevated levels of
adrenaline and dopamine which could in turn stimulate your sex drive
and its related process. hence the term POST DEPRESSION EXCITATORY
REBOUND.  if you drik heavily regularly long enough regularly enough
you will probably be overstimulated to point of morning shakes or even
seizures as can be the case with chronic alcoholics.