I am not medically trained at all but please make an appointment with your gp , the same thing happened with my husband and he ignored it , it only happened one time and he put it down to his high blood pressure and diabetes.  He was wrong he was diagnosed with kidney cancer last month . Consult your doctor,  better to be safe than sorry 

              Wendy 

Hi Pandabear. Welcome to the forum.

Passing blood in your pee or poo, without an explanation, is something that shouldn't be ignored. Usually, it's something simple and harmless, but why take the risk?

Just before Easter I passed blood in my water on just one occasion. I saw my GP, who referred me to a consultant. It turns out I had the beginnings of a bladder cancer.  I had a very simple operation (TURBT) and was back home the same day. All being well that should be the end of it.  Because I didn't ignore the warning, it was caught early, which is always good for cancer.

I'm not saying that you have cancer, but best get yourself checked out.