Green’s Dictionary of Slang

1. (US) an eccentric.

[1575-83		‘Bashe Libel’ in May & Bryson Verse Libel 80: Whether his filthy, feltred beard / Be fitter to serve a dizzard].
1963		(con. 1930s) D. Tracy Brass Ring 169: A real dizz, Kelly told himself unhappily [HDAS].
1972		B. Rodgers Queens’ Vernacular 65: What’s takin’ that diz so long? Is he dabbing A-20 behind his ears?
1984		Algeo Stud Buds and Dorks 7: An absent-minded or inattentive person [...] diz, dope [HDAS].

2. (UK black) MDMA in crystal form.

2017

hubpages.com ‘Roadman Slang 10 Jan. 🌐 Dizz - MDMA crystal.