WTF just happened??

So I started my cycle it was about 5 days late and it was light as usual. However the next day I had a gush of blood come out and there was a huge blood clot. I was at work and was told to leave and go to the ER. Which I did. Inbetween me leaving abd getting to the ER I used the restroom and there was nothing but blood clots mixed with urine. The ER just made me pee in a cup. The results were negative so they sent me home. Never really addressed what was going on. But since that big gush of blood I have not bled again. My cycle is usually 3-4 days. This all happened on day 2. Should I be worried??