Bleeding at 16 weeks

I wanna know if this happened to anyone . I was at work and I was standing up and it felt like water coming out of me . I was not in pain no anything and I went to

Go check and my underwear was soaked with blood . So I went to the emergency room and when I got

Checked out and they did a ultrasound the doctor said the baby is fine and he see where I was bleeding but he said something like this happens and just goes away on it’s own . He classified it as unspecified I was so confused because I never heard of anything like it . It was so weird because when I got to the emergency room the bleeding stopped . I made an appointment with my OB to check me out Tuesday but I am not bleeding heavy no more the blood is brown and I’m fine . This just really scared me and It was nothing wrong with me and the baby I am glad .