European Commission President Jean-Claude Juncker arrives for the second day of a North Atlantic Treaty Organisation summit in Brussels, Belgium, July 12, 2018.
He later said that Mr Juncker "attended the dinner normally and then the pain disappeared" and went on to complete his full schedule of events on the following day.
The president had suffered a "very particularly painful attack of sciatica accompanied by cramps", Mr Schinas said. Portuguese Prime Minister Antonio Costa said Thursday that Juncker had complained of back pain. He publicly said that these seizures may be affecting his ability to walk, luckily this did not happen.
Sciatica is a common condition that affects the sciatic nerve, which runs from the hip to the foot.
Sciatica is pain and numbness in the backside and legs that can cause difficulties walking. That was unfortunately the case Wednesday night, ' Schinas added. President of the Czech Republic Milos Zeman and President of Ukraine Petro Poroshenko assisted him when he lost his balance as he was speaking to Dutch Prime Minister Mark Rutte.
'He is taking medication and feels better'.
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Mr Juncker, whose five-year term at the head of the commission ends next year, has faced questions before about his public demeanour.
The spokesman also blasted "insulting headlines" that were "exploiting president Juncker's pain". "I don't think this is elegant and I don't think this is fair", Schinas said.
Asked whether Mr Juncker had mixed painkillers and alcohol, Mr Schinas replied: "No he didn't - at least I am not aware of this happening".
German Chancellor Angela Merkel's spokesman Steffen Seibert said the government had "high" confidence in Juncker, in reply to a question about Juncker's ability to conduct trade talks in the USA, for example.
Juncker also teased Hungary's hardline rightwing Prime Minister Viktor Orban over his strongman reputation, jokingly greeting him as "dictator".