What Causes Discoloration And Numbness At The Tip Of Index Finger?

Just today, my right index finger tip has experienced complete numbness twice. The second instance, my finger also turned blackish blue. Should I be concerned about anything serious? Should I call my doctor? I had this happen not that long ago except that my finger stayed black and blue for a couple of days. I went to the doctor and he said I probably just hit my hand on something.