Question about medals

[Walt Whitman]

When you do something to attain a medal, what causes them to disappear over your head? A certain lapse of time, getting killed, or something else? When you get a new medal for doing something, does the old one disappear over your head?

[Fjoggs]

They disappear after a certain amount of time. The new one appears when the old one disappears. (AFAIK)

EDIT: Eh, that last sentence is kinda duh. What I meant was that the new one appears after the old one has been there after the same time it takes for it to change on your own screen. (If you got the medals.)