A bracket is a small, relatively smooth object. Swallowing one isn't a problem. It's biologically inert, you can't feel it as you swallow, it doesn't get stuck in the digestive system and it passes out of the body without any trouble, without you even noticing. You don't need to seek medical help if you've swallowed a bracket.
This answer is for general information. Your own case needs an examination by an orthodontist.