Showing Naked to the stars by Gordon R. Dickson

During an action on the third planet from Arcturus, soldier Cal Truent woke up in the hospital with a sixteen-hour hole in his memory. No one knows what it is that Cal has forgotten, but his superiors can't take the chance that it might be something deadly to his fellow soldiers - and to Earth.
Somehow Cal means to seek out whatever it is that his mind is resisting . . .