Don’t have a loose chain

Last Saturday I busted my mouth open in a place. I was cycling on my BMX bike when disaster struck, as I was talking to myself as normal when I noticed my chain was rattling. I thought nothing of it because I was turning to go home now and me and my dad could check it out once I was home. I was about half way home and at full speed with my feet on the pedals when… CLICK!!! The chain had slipped off the cog and had jammed the wheel. I was on a road past a small cluster of about three houses. I had went from full speed to full stop in quarter of a second. I was thrown forward over the handlebars and face planted onto the rough stone of the road. I later found out it was all because of a loose chain.