Now everyone calm down. During genital retraction syndrome, the genitals do not actually retract:

Aside from the emotional distress, koro by itself is not physically harmful, and no actual retraction takes place. Injuries have occurred when stricken men have resorted to apparati such as needles, hooks, fishing line, and shoe strings, to prevent the disappearance of their penises.

There has been a recent outbreak in Nigeria.

An epidemic struck Singapore in 1967, resulting in thousands of reported cases. Government and medical officials alleviated the outbreak only by a massive campaign to reassure men of the anatomical impossibility of retraction together with a media blackout on the spread of the condition.