Mrs Merkel’s body shook as she stood with Finnish PM Antti Rinne while watching military honours in Berlin to mark his arrival.
In a news conference after the incident, the German chancellor insisted she was “fine”.
“People don’t need to worry about me,” she added. Mrs Merkel was first seen shaking uncontrollably during her reception of Ukraine’s president Volodymyr Zelenskiy in Berlin on 18 June, but later said she felt better after drinking some water.
Mrs Merkel was seen shaking again as she met German President Frank-Walter Steinmeier on 27 June in her second such bout within two weeks.
Her spokesman said at the time she was fine and she later headed off to Japan for the G20 summit.
After her Japan trip, Mrs Merkel went straight into three days of tortuous talks in Brussels to decide on a new group of nominees for top European Union jobs – a package that has strained her coalition government.
In the past, she has joked that she is a “sleep camel” who can go days with just a few hours of sleep as long as she gets a full night of sleep at the weekend.
She is due to go on holiday later in the summer.
Merkel, 64, has been at the helm in Germany for 14 years. She announced last year that she will step down as chancellor when her current term is finished in 2021.
The chancellor, who is renowned for her work ethic, has no history of serious health issues.