Joe Biden awoke suddenly in his hotel room, curled up on the floor and fully clothed, and felt an electric surge inside his head, “a rip of pain like I never felt before,” as he later recalled. It was 4:10 a.m. on a winter day in 1988.

The debilitating headaches had been happening for nearly a year, interrupting his first presidential campaign as the 45-year-old Biden popped up to 10 Tylenols a day. He had been diagnosed with a pinched nerve and for a time wore a cervical collar. Now, as he lay on the floor of his hotel room in Rochester, N.Y., the pain was even worse. His legs felt dead, and he struggled to turn his head.