If it comes from below - bad, if it's a sidestream from your nose - don't worry. Happened to me once while showering, I was spitting blood all of a sudden. I didn't realize I was bleeding from the nose, which is normal if you're cool like me.
A few people I know have gotten hooked on energy drinks and as a result given themselves lesions in the lining of their stomachs causing the symptoms you describe. Otherwise known as a 'bleeding ulcer.' Examine your diet.