Open Question: Enlarged penis vein after masturbation?

I was masturbating and once i finished one of the veins on my penis was enlarged and i could move it around a bit from right to left. 5 mins later it went down then came back down and now its gone. I was masturbating really intensely and kept going even after ejaculation which have maybe been the cause but what is it from and is it anything to worry about? I have not had any sexual relations any time soon so its not an STD. Thanks,