Britain has had a famous list of sufferers, none more so than Winston Churchill (right) who would refer to the beast as the "black dog". Harold Macmillan was another prime minister to be afflicted, never able to escape "the inside feeling that something awful and unknown was about to happen". Some found respite in drink; Macmillan found his in "going away for a few days" to read Jane Austen. Lord Steel of Aikwood (left), the former Liberal leader, is among contemporary politicians to have had bouts of depression.
At least one in 200 people suffers from clinical depression. The nature of their job, however, makes politicians especially vulnerable. Few trades cast their practitioners so brutally from the elation of electoral victory and untrammelled power to defeat and nothing.
Abroad it is no different. The Russian President, Boris Yeltsin, is similarly afflicted. Just as Churchill's worst bout of "Black Dog" came after he was ejected from the government during the First World War, Mr Yeltsin reached his nadir after being disgraced by Mikhail Gorbachev in November 1987.
"I would sleep three or four hours a night and then the thoughts would come creeping back," he wrote in his autobiography Against The Grain. "Everything about me was burnt out, everything within me was burnt out." Twice, according to his former bodyguard Alexander Korzhakov, he tried to commit suicide.
After being cast into darkness by the Mr Yeltsin he despised, Mr Gorbachev himself would display some symptoms of the malady. So did even that most nonchalant of men, George Bush, after his presidential defeat by Bill Clinton in 1992, which he never believed could happen.
Among this distinguished company, Mr Bondevik's service is to have owned up to the condition while he suffered from it, in office, and to seek medical advice to deal with it.