Character Analysis
On the day of the Hiroshima bombing, he was a young surgeon working at the Red Cross.
Where He Was When It Happened
He was on his way to the lab to deliver a blood vial when the bomb went off. He somehow managed to be ideally positioned within the hospital to be uninjured (though the vial of blood he was carrying did break). He ended up being the only doctor in the hospital who was uninjured.
What Happened Next
He spent the next several days working more or less nonstop in the hospital. He was totally exhausted, but his one attempt to catch a couple of Z's was a massive failure:
By three o'clock the next morning, after nineteen straight hours of his gruesome work, Dr. Sasaki was incapable of dressing another wound. He and some other survivors of the hospital staff got straw mats and went outdoors—thousands of patients and hundreds of dead were in the yard and on the driveway—and hurried around behind the hospital and lay down in hiding to snatch some sleep. (3.10)
Eventually, he decided he had to head home to his mom's house to let her know he hadn't died in the explosion. He slept for seventeen hours.
Afterthoughts of War
In the longer term, he stayed at the Red Cross for a while, but then eventually he decided to open up his own private clinic in Mukaihara. According to Hersey, despite being a doctor and hibakusha, Dr. Sasaki didn't really pay much attention to the lasting health effects of the bomb that were popping up in the medical literature. Instead, Hersey implies, he avoided thinking about the bomb and its impact: "In his town in the hills, he treated few hibakusha. He lived enclosed in the present tense" (5.39).
While he was visiting a Red Cross hospital to get some refresher training, he got some medical tests done, and they discovered a "shadow" on his lung. In the end, he had to get that lung removed. Hersey does not comment on whether Dr. Sasaki's tumor was related to the Hiroshima bombing—but since his reference to Dr. Sasaki's medical woes came soon after an extensive laundry list of the health effects hibakusha typically experienced, it's hard not to see a possible connection between the two…
Anyway, we'll leave the medical detective work aside. Dr. Sasaki reported that he found this whole experience with his lung even more life altering than the Hiroshima bombing; it entirely changed his attitude toward his patients, and he became more compassionate and attentive as a result:
In later years, Dr. Sasaki came to think of that experience as the most important of his life—more important than the bombing. Haunted by the loneliness he had felt when he thought he was dying, he now did his best to move closer to his wife and children—two sons and two daughters. An aunt startled him one day by saying, "You are lucky, Terufumi. After all, i wa jinjutsu—medicine is the art of compassion." He had never thought about the meaning of this saying, which is held up before all young Japanese training to be doctors. He determined thenceforth to be calm and composed, and not leave undone anything he could do for a patient. (5.43)
Kind of interesting that a health crisis had a bigger impact on Dr. Sasaki's worldview than the bombing itself, right? Of course, it kind of makes sense, since Dr. Sasaki actually came much closer to death with his health crisis than the atomic bombing.
In any case, Hersey suggests Dr. Sasaki's experience as a critical patient definitely made him a better doctor going forward.
Dr. Sasaki's Timeline