HALF-LIFE: Reflections From Jerusalem on a Broken Neck. By Joshua Prager. Byliner ebook. 132 pages. $3.99.

Joshua Prager was 19 in May 1990, a young man moving fast toward the man he would become. He added 4 inches to his frame the previous winter, banged the rim when he grabbed rebounds, decided he would go into medicine and just before a trip to Israel, made peace with his father, a strong-willed doctor, celebrating the moment with a game of catch.

Then in Israel, a runaway truck plowed into the rear of a bus he was riding in, leaving him half-paralyzed.

In “Half-Life: Reflections From Jerusalem on a Broken Neck,” Prager writes with heart and marrow about what it’s like to suddenly become disabled, or as he put it, “divided like the spine of a book.” But Prager’s compact and important e-book is about something more than the challenges of disability: It’s about what happens to a person’s identity when his or her world is turned on its end.

After the collision and college, Prager eventually would write features for The Wall Street Journal on subjects as disparate as the mysterious author of “Goodnight Moon” to the anonymous person who won a Pulitzer Prize for photographing an Iranian execution.

Over time, he realized that many of his stories involved secrets and that something inside himself remained unexamined.

In his quest for answers, he writes about his life before and after the wreck, of enemas, walking canes and budding romances snuffed by fears, his and others.

He shows what it’s like to lose a life he expected to live, and the thrill of finding new paths.

“I know that even more dangerous than to live is to not live — to not feel the sun, to not climb the stairs, to not drive off alone, to not wade into water, to not head to sea, to not join the crowd.”

As with most good memoirs, we learn from “Half-Life” about our own assumptions as we experience how Prager manages his own moments of uncertainty.

His search ends with an unlikely twist that raises fundamental questions about the malleability of identity when it collides with life’s inevitable shocks, and how the absence of self-analysis can be a hobbling disability in itself.

Reviewer Tony Bartelme is a reporter for The Post and Courier.