A bump or blow to the testicles can cause severe pain and feelings of nausea and may even cause someone to be sick. These feelings should pass quickly and it is best to lie down and try to relax until it passes. If the pain continues or you notice any swelling, you should get this checked out by the doctor. In some cases, the blow can result in fluid building up around the testicle (hydrocele), or the testicle twisting (torsion).
Torsion usually affects younger boys and requires emergency treatment to help with pain relief and save the testicle. The twisting of the blood vessels, which supply the testicle, causes the pain and this pain develops very quickly. If not treated within six hours the testicle may have to be removed.