On page 301 of President Nixon: Alone in the White House, Richard Reeves tells the following story:
February 3, Nixon canceled an NSC meeting and called in Kissinger,
Haldeman, Mitchell, and Connally. After more than an hour, the
President went into the small study off the Oval Office and stripped to
his underwear, listening to the others as his chiropractor, Dr. Kenneth
Riland, manipulated and massaged his back. Then he came back into the
discussion wearing only underpants and sat down, telling Kissinger and
Haldeman to issue the order: phase two, the ARVN invasion, was 'Go.'"