2 year old dental implant. bit down on a nut and now it feels like it's loose - like if i ate something sticky it would come off. am i doomed?

Doomed, no: But you need to immediately have it examined by your restorative dentist. If it is cemented, it may have debonded. If is is screwed it, the screw may be loose. In very rare cases the implant or the screw holding the crown/post to the implant may have fractured. The sooner you have it looked at the better off you will be in the long run.

Not Necessarily: If the implant is lose/moving, then (sadly), it is "doomed." However, if the crown or abutment (connecting piece) are loose, then it can be fixed (often quite easily). The key, however, is this: the longer you wait to see your dentist and find out what's going on, the more likely you are to actually BREAK something...then it will be hopeless. So, see your dentist immediately! No chewing 'til then.