Actually I made a mistake its 2 MM, not CMs.
Even so, it's probably not significant. Show a doctor to be sure.
Dr. Rockoff
2 cm is a pretty big mark. It seems hard to believe it was there long without your noticing it. A mark that big that comes on that quickly is probably secondary to trauma--perhaps the skin was scratched in your sleep or something.
If the mark is painful don't wait to show a doctor. But if it's just there, and not bothering you, I would wait 2-3 weeks. If the mark hasn't gone awy by itself, show a doctor.
Best.
Dr. Rockoff