Death Dimension — Denis Hughes

When airline pilot Robert Varden's plane is wrecked in a thunderstorm, he goes to bail out. As he claws his way through the escape hatch, he is struck by lightning and his consciousness fades into oblivion. Miraculously, Varden cheats death, and awakes in hospital after doctors succeed in saving his life. But he emerges into an unfamiliar world that is on the brink of a devastating war, and where his friends are mysteriously seventeen years older than he remembered them...