It is possible for people to develop a stress fracture in the metatarsal bones with no specific injury. This is often due to increased activity such as training for a long run. It can also be due to other issues such as foot shape. The important thing here is to diagnose the problem
Treatment usually consists of rest, ice and elevation of the foot. It is very uncommon that surgery is needed for this problem. See here for further info: http://orthoinfo.aaos.org/topic.cfm?topic=a00379
Recovery takes around six weeks.