Jimmy Kimmel is either psychic or has the unluckiest timing in comedic history ... last Tuesday, he made a joke about Rudy Giuliani rising from "the grave" -- just days before we learned the former NYC mayor was hospitalized.

In his monologue, Jimmy quipped about Giuliani coming back from the dead, saying ... "So last night, America’s mayor, Rudy Giuliani, rose from the grave to weigh in on the ongoing drama involving me."

This came up because he was ironically referencing another coincidental crack he'd made ... about Melania Trump looking like "an expectant widow" ... two days before the alleged assassination attempt at the White House Correspondents' Dinner on the night of April 25.

A spokesperson for Giuliani announced in a statement Sunday Rudy was in the hospital in "critical but stable" condition.

No word yet on what exactly landed him in a Florida medical center ... but this is the second time Rudy's been rushed to the hospital since September.