Sleepy when you shouldn't be - three takes on sleepiness in the workplace

On your way to work this morning were you bright-eyed and alert? (This doesn't count if it followed consumption of two double-shot long blacks). Or were you a little drowsy, with heavy eyelids, letting a yawn or two escape? We've all worked while we felt sleepy, for one reason or another, but when does sleepiness become risky and are we ever too sleepy to work? If we are, how do we get treatment and when are we ready to get back t...