Green’s Dictionary of Slang

willies n.

also willeys, williwalloos
[ety. unknown, ? link to fig. use of dial. willy-wambles, stomach-rumbling]

1. [late 19C+] nerves, worries, tension; esp. in phr. give (someone) the willies, to unnerve, booze willies, delirium tremens.

2. (US drugs) withdrawal symptoms from narcotic drugs.