It's a happy tune about a hangover that comes after 5 days of heavy drinking.
Madness string 16472
It's even scarier that it's a disease - it'd be one thing if it was 'a demon did it', but that's understandable somehow. A disease is brutally mechanical, which to me is scarier.
Post-Awareness Stage 4 is where serenity and the ability to recall singular memories gives way to confusions and horror. It's the beginning of an eventual process where all memories begin to become more fluid through entanglements, repetition and rupture.