Green’s Dictionary of Slang

swellhead n.1

[SE swell + head]

1. a drunkard.

[US]‘Ned Buntline’ Mysteries and Miseries of N.Y. I 116: ‘Swell-head.’ A bloated drunkard.
[US]Wilmington Jrnl (NC) 29 Mar. 5/3: A swell-head came [...] he had an empty bottle, and his noise was like a cancer.

2. (US black) one who has passed out through drug use.

[US]R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].

3. see bustskull under bust v.1