It's just possible you are thinking of the introduction to part five of Blue Mars by Kim Stanley Robinson. It isn't in the opening pages, though it is an introduction to a part of the book.
An old man sitting at sickbed. Hospital rooms are all the same. Clean, white, cool, humming, fluorescent. On the sickbed lies a man, tall, dark-skinned, thick black eyebrows. Sleeping fitfully. The old man is hunched at his head. One finger touches the skull behind the ear. Under his breath the old man is muttering. “If it’s an allergic response, then your own immune system has to be convinced that the allergen isn’t really a problem. They haven’t identified an allergen. Pulmonary edema is usually high-altitude sickness, but maybe the mix of gases caused it, or maybe it was low-altitude sickness. You need to get water out of your lungs. They’ve done pretty well with that. The fever and chills might be amenable to biofeedback. A really high fever is dangerous, you must remember that. I remember the time you came into the baths after falling into the lake. You were blue. Jackie jumped right in— no, maybe she stopped to watch. You held Hiroko and me by the arms, and we all saw you warm up. Nonshivering thermogenesis, everyone does it, but you did it voluntarily, and very powerfully as well. I’ve never seen anything like it. I still don’t know how you did it. You were a wonderful boy. People can shiver at will if they want, so maybe it’s like that, only inside. It doesn’t really matter, you don’t need to know how, you just need to do it. If you can do it in the other direction. Bring your temperature down. Give it a try. Give it a try. You were such a wonderful boy.”
The person in the sickbed is Nirgal, who is ill because he has returned to Earth only to be felled by allergies.
I suppose it's possible you might have found part five of the book published separately as an extract, or as a serialisation.