I went down the water slide and after wards my lower abdomen was cramping. What happen?

Coincidence? Strain? Perhaps it's just coincidence? Or perhaps you sustained a muscular strain from too much laughing (seriously!) or twisting while going down slide. The latter is more likely if you don't have a strong core and then tightened up during your trip down. If it doesn't go away in a day or so, go see your doctor. Go see ur doc immediately if any fever, painful urination, bloody urine, nausea/vomiting etc.