For the past eight months he has more or less managed to behave himself. He has begun to look like a fairly conventional world leader, visiting a fellow president here, firing off decrees there, sacking the odd errant official and generally trying to instil a mood of order in his chaotic land.
It was possible to imagine a measure of stability had arrived in Russia, silencing those alarmists who persistently foresaw revolution, fascism or just total collapse. But the vertical hold has begun to flicker. Once again, Mr Yeltsin's public appearances summon up stomach butterflies, a perilous sense that anything could happen. The president again seems to be walking on quicksand, while his aides scurry anxiously in his wake, hoping to break his fall.
This new mood has unfolded in a seven-day spell which began with his strange performance in Sweden and ended with him languishing, yet again, in the Barvikha sanatorium outside Moscow. Although his physical condition may not be serious - he has, let's admit it, been written off by the press far too many times - there is a worrying sense that something deeper is amiss.
By any standards (even his own) Boris Yeltsin's Stockholm performance was extremely odd. He promised unheard-of disarmament offers, invented on the hoof. He claimed Japan and Germany had nuclear weapons, an alarming misconception in one whose country's history has been so painfully entwined with these two nations, and who happens to be in charge of one of the world's largest nuclear arsenals. He interrupted a meeting with King Carl XVI Gustav to bawl out two members of his entourage. At one point, he appeared to think he was in Norway.
The Swedes were not impressed. "This VIP breaches protocol, tears his colleagues off a strip in front of the world, talks - let's state it frankly - confused nonsense on international issues, and carries himself in just the same stiff and drug-induced way that we got used to seeing from Soviet leaders in days long gone," wrote the Svenska Dagbladet.
Nor were Russians much amused. Eleven years ago, mention of Mr Yeltsin's name to a Muscovite was frequently met by warm praise for the populist leader, the former construction boss who stood in the bread queues with ordinary folk and fought the privileges enjoyed by the party fat cats.
Two years ago, it would evoke a snort of anger with the president, who led them into a terrible war in Chechnya and whose cronies were stripping the country bare. Now they simply shake their heads and point to their temples. The president, some believe, could be ... well, a kopek short of a rouble.
This is, of course, almost certainly unfair, as the vox populi usually is. The truth is that we are witnessing, not a departure from the norm, but a return to it. Boris Yeltsin's career has always rattled along a helter-skelter of triumphs, disasters and erratic behaviour, born of an infatuation with the limelight and a kamikaze temperament.
On the one hand, there is the Boris Yeltsin astride a tank in Moscow, brilliantly defying the coup plotters of 1991. On the other, there is the Yeltsin who, three years later, drunkenly conducted a German police band in Berlin, singing a song that bore no resemblance to the one the musicians were playing. In the last few days another two contradictory snapshots have landed in the Yeltsin album: three days after his Swedish debacle he appeared in the Russian parliament, heartland of the enemy opposition, and masterfully bamboozled it into passing the budget on the first reading.
Outbursts of bizarre behaviour have punctuated his political career with the regularity of tantrums in a two-year-old. One respected Russian commentator, Dmitri Trenin, has compared him to a small boy who always wants to do something which will stun or please his audience.
In Russian politics, this condition is barely a disadvantage, as there is no system of accountability. Yeltsin has no party to offend. When it matters, electors can be herded one way or the other by the mass media, which is controlled by a few generally supportive tycoons. As power is concentrated in the president's hands, the opposition can bleat away to its heart's content, but can do little. It is a political stuntman's paradise, as the ultra-nationalist and self-publicist extraordinaire, Vladimir Zhirinovsky, has demonstrated.
Not much prevents Boris Yeltsin from saying what he likes - a fact rarely appreciated by his foreign audiences. Had Bill Clinton behaved like Mr Yeltsin in Stockholm, there would have been a volcanic political eruption back home, whose fall-out would have continued for months. No such fate awaited the Russian president. They were just words, and words here don't really count for much. It was Mr Yeltsin, remember, who told the Soviet republics to "take as much sovereignty that they can swallow". A few years later he flattened Grozny.
Such conditions are a happy circumstance for Mr Yeltsin, given his disposition. Attention-seeking bellows out of the pages of his highly ornamented and self-flattering autobiographical writings. We meet Boris, the peasant kid who was so surly at school that he was thrown out, only to return to perform spectacularly well; Boris the Brave, who rescued his chums when they all fell ill while out on a trek; Boris the Stupid Show Off, who blew off two of his fingers playing with a hand grenade.
That pattern carried on in adulthood. Spectacular public victories and theatrical defeats have been interlaced with genuine accidents. His biographers still puzzle over the extraordinary night in September 1989, when he ended up getting a drenching in the Moscow River, then disappeared for a fortnight.
He has indicated that it was an attempt on his life in which he was shoved off a bridge by thugs apparently working for his rival, Mikhail Gorbachev - although Moscow's assassins tend to be more efficient than this. His estranged and vengeful confidant and bodyguard, Alexander Korzhakov, says it was one of two suicide attempts, a measure of his regular bouts of gloom. The other supposedly happened when he locked himself in the banya (Turkish bath).
These days such crises tend to lead Russians to conclude (without much censure) that he was probably drunk at the time. Similar whisperings have now been renewed about the Sweden gaffes, although that seems unlikely. His current advisers, including his daughter Tatyana, seem too shrewd to allow him off the leash. Gone are the unsavoury band of generals who formed his drinking buddies - Mr Korzhakov included. And these days his heart doctor, Renat Akchurin, is a constant companion on his trips.
His handlers do, however, appear this time to have failed to stop him running himself into the ground, a tendency which he has displayed all his life and which may well have been the cause of his behaviour in Sweden. Even they cannot tame his manic approach to work.
He is the polar opposite to the five-hours-a-day-and-not-a-second-longer Ronald Reagan. He operates like an undergraduate who does nothing until the day before finals, and then launches into an all-night cramming session before collapsing in exhaustion. When coronary trouble put him out of action in late 1995, he bounded back with a whirlwind election campaign the following year. He was proud of his breakneck approach, boasting of getting up at 5am every day and working well into the night. Until, that is, he had another heart attack and disappeared again.
After his quintuple coronary bypass in November, he returned, only to be sidelined by double pneumonia in January. Then he came roaring back once more, grabbing back power and limelight from his minions, whom he dominates by a policy of divide-and-rule. Although he looked much older than his 66 years, no one - but no one - imagined he would display such energy.
Another motive must also be factored in. Boris Yeltsin is thinking about his place in history, a legacy complicated by his indefensible role in the Chechen war, which he regards as his worst mistake and which will be seen as an eternal blemish on his record by many. Russian law (though ambiguous in Mr Yeltsin's case) only allows a president two terms; he has said several times that this is the final stretch, although in reality he probably has yet to make his mind up. If he does step down, time is running short to set the record straight.
He is also doubtless eager - for sound political reasons - to ensure Russia slips no further down the global pecking order, a perception reinforced by what is seen here as Nato's over-hasty expansion into the east. Thus the rejoicing in Moscow when Russia brokered a deal with Iraq, averting the crisis over UN weapons inspectors. Thus, too, his packed foreign diary. In the past three months, there have been meetings with Tony Blair, Helmut Kohl, Jacques Chirac, the Japanese prime minister, Ryutaro Hashimoto, China's Jiang Zemin and others.
Add to that a domestic political crisis involving accusations of corruption against his right-hand man, Anatoly Chubais, and the plethora of other Russian problems - a coal mine explosion, an air crash, millions of unpaid workers and pensioners, a nosediving stock market - and there's little wonder that he looks exhausted.
So what can we expect now? This could, of course, be it: Moscow was seething with rumours at the weekend about Mr Yeltsin's health. Just as likely, though, is more of the same. Boris drops out of sight for Christmas and the New Year, then, just as we are wondering what is happening, he bounds back, only to crash in a heap six months later. Which is why you have to ask the question: what the hell is wrong with the man?