Is R Subcostal Fluid Build Up A Dangerous Situation?

I what appears to be a pocket of fluid, around 8 cmm. in the upper right quadrant of my abdomen. It is visible as a slightly raised area versus the other side. The exact term from my doctor was R Subcostal fluid buildup. It appeared suddenly last Sunday evening or Monday morning, around the time I went for a sonogram to check out what my doctor thought might be a periumblical node or cyst. That turned out okay - a cyst or fatty tissue, all of my organs showed clear as much as could be told by a sonogram. But, the radiologist saw the fluid build-up; he kept asking me if I had injured myself, I didn't think I had although I had been sweeping up leaves the night before and stretched pretty aggressively a couple of times. I was nervous the morning of the sonogram and was holding myself very rigidly. I also had to go to the bathroom.