Read MoreDollar hammered amid Fed; euro at $ 1.10
In fact, in his newsletter Wednesday morning before the Fed’s statement, Gartman said if the euro got to $ 1.0875-$ 1.0925, he’d start thinking about selling.
The euro surged above $ 1.10 after the statement. The common currency’s one-day gain against the dollar was its largest since March 2009. It had dropped below $ 1.05 for the first time in 12 years earlier this month.
Gartman called the swift moves “amazing.”
“I’ve been trading foreign exchange for 45 years, and other than the …weekend after the Plaza Accord, I cannot recall a day when we saw that many big figures go flying by.”
The 1985 Plaza Accord was an agreement between the G-5 nations to depreciate the U.S. dollar against the German mark and the Japanese yen.
Read MoreDovish Fed whipsaws markets
—Reuters contributed to this story.