Hello. Welcome to Healthcare Magic. Although it isn t possible to diagnose your condition without an examination, it sounds like you may have a communicating hydrocele, which is a pocket of fluid that collects beside your testicle when you re upright and then disappears when you lie down. The fluid that collects in a communicating hydrocele originates in your abdominal cavity: when you re standing or when you bear down the fluid follows a weakness in your groin, percolates through a thin channel leading to your scrotum, and collects beside your testicle. When you lie down, the fluid goes the other way, allowing the hydrocele to shrink. Hydroceles aren t cancerous, and they usually aren t dangerous. However, the weakness in your groin that permits the fluid to pass through could also admit a loop of intestine, causing a hernia. Therefore, if you do have a communicating hydrocele it might be wise to get it repaired. A urologist (a doctor who specializes in the genitourinary tract) can help you with this. I hope that helps, and good luck!