Green’s Dictionary of Slang

1. energetic, excitable.

1934		Wodehouse Right Ho, Jeeves 97: Bertram, so far from being the victim of despair, had never felt fizzier in his life.
1949		Wodehouse Mating Season 11: A singularly fizzy bird, as a rule.
1954		Wodehouse Jeeves and the Feudal Spirit 59: The days that followed saw me at the peak of my form, fizzy to an almost unbelievable extent.

2. (S.Afr. drugs) of a cigarette, containing marijuana.

1963

L.F. Freed Crime in S. Afr. 275: At these parties there were a lot of actors, actresses, and musicians who were nearly all drug-addicts [...] and smokers of ‘fizzy’ cigarettes.