Ford Focus speedomoter

the speedomoter on my car just stopped working today. i shifted down to 3rd gear on a steep hill and noticed the speedo went down to 0mph. the speedo remained on 0 for about five minutes and then began flicking up and down sporadically. hitting bumps on the road seemed to alter the performance of the speedo as if suggesting a loose connection? after about 20 more minutes the speedo returned to normal and remained so for the remainder of my driving time that is until i stopped and restarted the engine again after being in a shop. at no time during the drive when the speedo was dead or acting sporadically was the engine performance affected. do you think this could be a simple wiring problem or a deeper underlying problem that will lead to a multitude of other problems?