Bleeding gums are not normal. This can be a sign of gum disease. It starts out as gingivitis, a early stage of periodontal disease. Like many disease this can go undetected. Gingivitis is caused by the bacteria that is found in plaque (the soft white film that accumulates on your teeth). When plaque sits on your teeth too long it starts to irritate the gums. Causing them to become inflamed and some times bleed. If the plaque is not removed routinely with brushing and flossing it will harden to the teeth, becoming tarter or calculus. Once this happens the only way to remove it thoroughly is by having your teeth professionally cleaned.
When gingivitis goes untreated it will eventually turn into periodontal disease. This is where bacteria causes the gums to swell open and the bacteria reach the bone. Once it reaches the bone the body tries to combat the infection by receding the bone. Bone is what holds the teeth in. Once enough bone is deteriorated your teeth can become loose. With periodontal disease there is no way to grow the bone back. We can only maintain the gum and bone health. If too much bone is gone teeth may not be able to be saved. Periodontal disease can go undetected for many years. It is not something that hurts or you can feel.