Hopefully not, but sounds like a classic example of a tendon/ligament tear (rupture...including the heavy discoloring which is due to broken blood vesels). If there is a bulge , around the area, than that may confirm it even more. Some times pain, though usually not much afterwards. Though , at times, a muscle knot (nerve clusters) it's self (somewhat common...no rupture/tear) will only require massage and hot/cold treatments.
Can't really treat something like that yourself, so seeing a doctor will be a good move (as you suggested). May, or may not, need surgery depending on the extent of the tear. Some will heal over time, though a longer time period. Good Luck.
