system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can quitting drinking kill an alcoholic?
gpt
With heavy/long-term use, alcohol creates big changes in the alcoholic's brain chemistry and body. When an alcoholic suddenly stops drinking, the brain's systems basically go haywire with the sudden change. Areas that were constantly excited by the constant alcohol are now pretty quiet, and other areas that were constantly quieted by the alcohol "wake up" and freak out, leading to seizures, heart strain, shaking, anxiety, etc. While that alone can be fatal, if the alcoholic has other health issues, the extra strain on the body can cause problems there and lead to death, particularly with underlying heart issues.

As an aside, a friend was just talking about this the other day and said that quitting alcohol is so dangerous compared to quitting other drugs because of how deeply the alcohol penetrates into the brain. Other drugs are slowed/stopped by the blood-brain barrier, remaining mostly on the surface of the brain or in the bloodstream, but alcohol is able to pass through.