Not sure why it does it but it is normal.

dear i am not sure its normal because i have heard this type of thing first time in my life so go to your doctor and consult with him.He will suggest you what should you do?

No, a few months ago my entire period was just some gross brown discharge that I would get in the morning but I wouldn't have anything for the rest of the day. I'm perfectly healthy and I was told that it happens sometimes. Since then I've had normal periods as well.

I think it just has something to do with old blood. Really, its nothing to panic about.

It could also be a sign of pregnancy, so please go test.