Don't panic! Your Twitter account hasn't been hacked, the password has just been accidentally reset.
Overnight, Twitter "unintentionally sent some password reset notices... due to a system error." Re/code reports that it has affected less than one per cent of Twitter users, but that's still a fairly significant number in absolute terms.
If you're currently locked out of Twitter, you should have received an email asking you to reset your password. Do that, and you should be back in business. At least it wasn't hacked, right? [Re/code]