If the time off contributes to his air of well-being, it also allowed him to play piano in public, something he hasn't done much of. Last November he played some Messiaen in a benefit concert for the magazine Index on Censorship, but, he suggests, a solo career does not beckon: "With me, it's very much a question of `Don't give up the day job.' Nobody's going to pretend that I'm a proper pianist. I can play the Elgar Piano Quintet, which has a great many notes, but I can't any more play the Brahms Piano Quintet; there are fewer notes, but they're not the ones that I can do.
"Still, it's lovely to be making the sounds for a change, and it's good to realise that often you tell your fingers what to do, and they look up at you and say `You have to be joking'. The principal cello and the leader of the Vienna Philharmonic have asked me to play a concert with them, so, God help me, I'm playing piano in the Musikverein next year."
Now, though, it's back to the podium, back to the City of Birmingham Symphony Orchestra (CBSO), back to a concert series that has occupied him throughout the last decade. Since 1990 Towards the Millennium has been Rattle's way (with help from others) of laying before us some of the century's greatest orchestral music, each year's concerts devoted to a different decade.
Rattle acknowledges that history doesn't conveniently divide itself into decades, but suggests, "The lateral view of history has been the ideal way to explore very different things. Take the 1950s: it was wonderful to play Stockhausen's Gruppen one week, an all-Bernstein programme the next; or, for the 1940s, to realise that Poulenc's opera Les Mamelles de Tiresias was written at almost the same time, in the same city as Pierre Boulez's Le Soleil des Eaux. Until Boulez told me, I had no idea that Poulenc went to the first performance of Le Soleil, and had written a very supportive letter. I simply put the two pieces together to annoy Pierre."
If a "lateral view of history" allows mischievous juxtapositions, it also highlights themes, affinities, oppositions. This year it's the turn of the 1980s, a decade of particular significance in Rattle's own career: in 1980 he took up the post of principal conductor with the CBSO, becoming its music director in 1990. That relationship (he calls it "a marriage") has been the foundation of Rattle's international reputation, and he is revisiting some of its highlights in this year's Towards the Millennium.
"A lot of people said, `When you get to the Eighties, you're not going to know what the hell to play. It's such a desert, isn't it?' But it seemed to me that in Birmingham it was a decade when we were very involved in getting certain works off the ground, works of which we gave first performances, or first British performances. That's part of the reason to include such different things as John Adams's Harmonium, Sofia Gubaidulina's Offertorium, Toru Takemitsu's Guitar Concerto, all pieces we were associated with."
Asked to put his finger on a Zeitgeist that might unite these and other works, Rattle responds warily: "It's difficult to provide soundbites about the arts, and I'm loath to do so ... except to say that it was a time of surprisingly emotional art of all kinds, with music moving back towards large gestures, and towards its audience. It was a time of political conservatism, and that still dominates political discourse; but it was also a time of extraordinarily positive development: the fall of the Berlin Wall or the influence of Solidarity in Poland, so that, for example - and much as he would have fought against the idea - there is no question that the optimism of the end of Lutoslawski's Third Symphony is something to do with what was in the air in Poland."
If there was a move towards the audience, it was not in terms of any easy "accessibility": among the works he and the CBSO are performing in Towards the Millennium is Nicholas Maw's Odyssey, a massive single-movement "super-symphony" lasting over an hour-and-a-half; another is Harrison Birtwistle's Earth Dances, which Rattle likens to "all the most difficult parts of all the Stravinsky ballets, played simultaneously. Over the years when the orchestra returns to pieces like these, we find ourselves wondering `How was this so incredibly difficult?"
The series reaches its climax, obviously enough, next year, when the CBSO joins with other arts organisations in Birmingham to present, not only the best of the 1990s, but also newly commissioned works. The orchestra will be able to afford to fulfil most of its commissions; others have been less fortunate in their funding. Although Rattle says, "It's a bore only ever talking about what money is available - I don't want to sound like a cracked record," he goes on: "One of the difficulties in modern Britain ... is that people don't realise that we have to plan ahead. If you want a new ballet from David Bintley at Birmingham Royal Ballet, it can't simply be done the week before. Most arts organisations are surviving, but the energy that goes into simply surviving means that we don't do as well as we might."
Rattle gave up the post of CBSO music director last year, and there have been suggestions that the shortage of funding in this country will be a major factor in sending him into the arms of a well-endowed foreign orchestra. Berlin has been mentioned, as have Vienna, Los Angeles, Covent Garden and Glyndebourne. Rattle seems content to bide his time: "I'll still be doing a lot of work in Birmingham, and the Orchestra of the Age of Enlightenment is my step-orchestra, if you like, but after 18 years in Birmingham it's wonderful to have time and space and I've realised that I've been chronically exhausted for at least three or four years. I was muddling along, but was it waving, or drowning?"
Whatever happens, this evangelical zeal will continue to work on behalf of the music, and the music-making, that matter to him. He's aware that both are threatened by the hegemony of the popular in all its forms, but special pleading is not his metier: "The debate about which is better has been unhelpful and desperately damaging. For my money classical music gives the most vitamins, but I wouldn't be without my Betty Carter records.
"It's not a matter of dumbing down, it's a matter of reminding people that they need classical music, and of persuading them to listen to modern music with respect. We should listen to everything. These days a young composer may have listened to Portuguese fado, or African music, or techno, and they're as likely to have been an influence as anything else. We're all going to have to be educators in the next century. It's not enough to perform and expect that people will come, to say `We have a right to exist'. The time for that is over."
Towards the Millennium opens on Saturday at the Royal Festival Hall, London SE1 (0171 960 4242); Sir Simon Rattle conducts the CBSO. Further concerts are in London and Birmingham Symphony Hall (0121 212 3333).