Scariest moment

So last week I went to the ER for heavy bleeding and I also passed a blood clot which I thought I was having a miscarriage due to the size of the clot. The ER sent me right up to L&D.. They did a full exam and ultrasound and my babies (having twins) we moving around and had strong heart beats. My boss told me not to come back to work until I see my doctor.. Went today they did another ultrasound babies are healthy and moving around and kicking alot. Still have no answers as to what caused the bleeding... Has this happened to anyone else?