Sleep, for a normal person, is divided into
Four Stages. The last two stages, 3 and 4, are what we call 'Deep Sleep' (scientifically known as
Slow Wave Sleep). It is during Slow Wave Sleep when the body, normally, releases ~50% of the day's dose of HGH. However, for an alcoholic, getting such sleep is most likely a pipe dream. Simply, the brain is drunk and sleep is a pretty complicated process. This means that the typical drunk sleep will be very light and most likely have little, if any, Slow Wave Sleep. If you add in middle-of-the-night withdrawals, when the
Depressant Effect of Ethanol wears off and you are left with a Stimulatory Rebound (waking you), as well as
REM Rebound (where
Rapid Eye Movement sleep goes from near non-existent to a level that's very intense, leading to all those bizarre nightmares that can bleed into wakefulness and cause hallucinations, etc), and so on… the bottom line is that sleep becomes extremely difficult, let alone Slow Wave Sleep.