It's not clear exactly what has happened beyond the fact that he is hospitalized.
The alleged suicide attempt was reported by a trash Norwegian "alternative" online newspaper inyheter based on their reading of off the record comments by Jaglands lawyer, who later said their story was misrepresented and that it was only a risk of suicide. The Greek newspaper serving as a source here mentions the (tabloid but at least somewhat reliable) newspaper Verdens Gang, who have only reported that he is hospitalized.
The Greek article is clearly not a reliable source, stating the following:
Norway’s Ministry of Foreign Affairs announced that it will request the Council of Europe to lift the immunity Jagland holds as a former Secretary General of the organization.
At the time their article was published the Council of Europe had already lifted the immunity, and Jaglands apartment had already been searched by Norwegian police.
Jagland was also never elected prime minister, he only held the post for a year after the resignation of Gro Harlem Brundtland until the following election. That's not a factual error or anything, but worth noting. He's more of a Theresa May than a Neville Chamberlain as far as Norwegian political history is concerned. His role at the Council of Europe and Nobel Committee was much more significant than his period as prime minister of Norway.