nope..
it cant get lost.. it just go farther up inside your uterous or whatever its called haha.. but it can get removed easily by your doctor in case u forgot u had one in and put in another.. but unless u didnt something get it pushed up more it wont naturally do that..
if this happeneded to u just go to your fmaily doctor (they wont tell your parents or anything! patient-doctor relationship) or to a clinic .. just be honest and tell them what happened (trust me doctors have seen EVERYTHING!) and they can help you out no problem!