Some of these questions now have answers. We know today that Mr. Brezhnev’s threat to send in troops was not the only crazy idea he had. At the height of the crisis, prodded by incessant pleas for help from Egypt’s president, Anwar el-Sadat (calls came in the middle of the night), the irate Soviet leader asked the Politburo to consider additional measures, like parking a Soviet naval force off Tel Aviv, or allowing Egypt to strike deep inside Israel with Soviet-supplied rockets.

These aggressive moves were very uncharacteristic of Mr. Brezhnev’s generally cautious approach to foreign policy. What happened? His daily schedule — recently declassified — tells a part of the story.

Since the outbreak of the fighting, Mr. Brezhnev often worked virtually around the clock, holding Politburo meetings during the day, receiving delegations at night and speaking to Cairo on the phone in between. On Oct. 22, he went to his favorite hunting lodge, Zavidovo, to recuperate. But according to his secretaries he stayed up at night, even calling his Kremlin office at 2 a.m. It was at Zavidovo that Mr. Brezhnev composed his letter to Mr. Nixon, and also his request to the Politburo, calling for tougher measures.

The letter was sent. But the tougher measures were quietly torpedoed. Someone in the Soviet leadership realized that the general secretary was going off the rails.

Then, on Oct. 29, the head of the K.G.B. (and Mr. Brezhnev’s eventual successor), Yuri Andropov, sent his boss a curious letter, warning him that the Americans and Mr. Sadat had conspired to overwork him by constantly keeping him engaged in difficult decision-making. This was “sabotage,” Mr. Andropov argued, pure and simple. The Americans and the Egyptians were trying to “keep us focused on the Arab-Israeli conflict, creating overstrain for all, and especially for you.”

Mr. Andropov knew what Mr. Kissinger did not: Mr. Brezhnev had developed an addiction to sleeping pills that, combined with alcohol, was undermining his ability to think straight. Mr. Andropov learned of the addiction weeks before the war in the Middle East but refused to intervene. Mr. Brezhnev’s erratic behavior during the war convinced Mr. Andropov of the dangers of inaction. Some of the details remain murky but Mr. Andropov and possibly other senior leaders evidently played a quiet role in keeping their country’s leader from sleepwalking into a world war.

Mr. Brezhnev soon recovered his mental faculties. The American escalation to Defcon 3 had a sobering effect on him. The last thing he wanted was a nuclear war with the United States courtesy of an unreliable, trigger-happy Middle Eastern client.