Definitely see a doctor, to be sure. If it happens more than once in a great while, then I would be more concerned.
But, I have also had this experience. I also went to a doctor. Absolutely useless, he was. I was tested for every STD in the book. Clean. And let me tell you, the chlamydia test was the worst thing I have ever experienced in a doctor's office before. I almost punched him in the face while he did it.
I find it happens, if it happens, after a big orgasm and if I have been drinking that night. I want to say the alcohol in the urine burns the residual semen in the tube.
Never thought I would type that sentence.
A trick I found to dealing with it is, when you experience it, stay upright. Either stand or sit until it goes away. Laying back down makes it more uncomfortable for me and seems to prolong the sensation. Go gravity!
Unfortunately, there is no quick fix I have found. Maybe it's like Tres said, a narrow urethra. If that is the case, then you just have to wait it out.