Black mark on gums between teeth. Freaking out.

Hi everyone. Firstly, its worth noting that I go to the dentist once a year, and have done as far back as I can remember. I dont drink fizzy drink and I rarely eat candy sweets (I sometimes have a bit of chocolate).

Recently (about a week ago) the battery died on my electric toothbrush, and until I got a replacement, I took to flossing a lot more than usual.

After two days I noticed a very small gap between my top middle teeth, which understandably, was due to flattening the little pointy bit of gum that lies between each tooth. This did not overly concern me.

However, the next tooth along from this, I recall vigorously cleaning between the teeth with floss. After a couple days, i noticed id flattened the little gum point between these too, and immediately stopped flossing. The problem is, where the gum has exposed a small area of tooth thats not normally seen, i find that it has a black looking stain under it. Does anyone know if this is normal considering an area is now exposed that wasnt before.... only right now Im imagining them telling me they have to pull my front teeth out or something. Its really stressing me out because it looks like i have a black poppy seed stuck there.

Anyone else had anything similar? I am due my yearly checkup at the dentist in a few weeks. I was just wondering if anybody could throw some light on it, to save me freaking out until i go to my appointment :S