Tony Blair puts himself under enormous pressure.
His leadership style - often criticised for being overly presidential - has always seen him taking on more of the burdens of government than most of his predecessors.
And in the age of 24-hour news and, as a result, 24-hour government, those pressures simply never end.
If the government wants to prove the seriousness of its intentions in any policy area, the prime minister has to be personally involved.
In everything from crisis "Cobra" cabinet meetings over issues such as foot-and-mouth to forging the breakthrough Northern Ireland peace talks, Tony Blair has been in the lead - often virtually around the clock and for weeks on end.
He has also chosen a particular, high-profile international role for himself that has seen him engaging in numerous lengthy, demanding and sometimes frantic diplomatic missions.
But over and above these self-imposed stresses, the prime minister has spent the past few months battered by the greatest pressures of his entire political life.
And probably worse for a man so used to winning, they have been overwhelmingly negative.
Spin, voter disillusion, loss of public trust, his presidential leadership style - all these things have dogged him for the past year or more.
Then there is the continuing row over reform of the public services, which shows no sign of blowing over.
But without any doubt, one issue has overshadowed all the others.
The war on Iraq, the frenzy of activity leading up to it and all that has followed from it has placed the prime minister under intense and often visible strain, both physically and emotionally.
Taking a country to war is always the toughest decision any premier can take.
Tony Blair took it against considerable international and public opposition and, thanks to his leadership style, to all intents and purposes, alone.
It is hard to think of a recent historical equivalent.
Since the war ended, of course, the pressures, far from lifting in victory, intensified.
Voters sent the prime minister their message in the Brent East by-election, which saw him losing a safe seat to the Liberal Democrats.
And his personal poll ratings slumped.
Then the prime minister had to address all these concerns as he delivered the most important conference speech of his political life.
He did it the day after Chancellor Gordon Brown reminded delegates that, should they by any chance ever be looking for an alternative leader, he had the qualifications for the job.
What all this amounted to was a real feeling for the first time in Westminster that Tony Blair's leadership might be at the beginning of the end.
The strains on the prime minister were clear to see - but since then they appeared to have abated.
But that was an illusion promoted almost entirely by the fact that media attention was diverted by the Tories' internal crisis over Iain Duncan Smith's leadership.
Even as that unfolded, the prime minister was under fresh pressure.
The Hutton inquiry heard from the top civil servant at the Ministry of Defence that Mr Blair chaired a meeting that started the process which led to the naming of David Kelly.
At the same time, the prime minister was attempting to end the crisis in the Northern Ireland peace process.
And he was at the centre of a new row over Europe, and demands for a referendum over the EU constitution.
And, of course, the Blairs have a young family.
Tony Blair has always appeared to handle the pressure of the job, but there have been signs that the stresses might occasionally get to him.
Most famously was his conference speech at the height of the fuel tax protests, when he briefly fell behind the Tories in the opinion polls.
His sweat-soaked performance then was seen as an indication that things were getting to him.
None of this means, of course, that the prime minister's health has suffered as a result.
There are any number of other possible causes for his ill-health.
Downing Street will want to reassure MPs and the public that what Mr Blair suffered was merely a relatively common condition.
And everyone on all sides will wish him a speedy and full recovery.
But few would argue this incident will not have lingering consequences for his leadership.