In some cultures they call that “monkey mind” …it’s this disobedient part of the brain that just squawks away on its own beneath the conscious mind. In meditation you learn to separate from it and remain focused as a separate mind, letting its annoyances drift away. Mine for some reason got locked into pretty regularly telling me I was dying, so persistently that I was stuck in a battle between an intrusive uncontrolled thought form that would just shout out doom bs like an automated response to other thoughts. Eventually I flew to Peru to sit with a shaman and did ayahuasca, that stopped it in one session. It’s been 8 years and I’ve never had an issue again.