Psychologist here...

Usually, heavy anxiety comes from childhood trauma - big traumas or small traumas.

Your mind keeps subtly playing back those traumas in various ways. One way is negative self-talk and/or self-loathing. This process can keep you in low level fear states.

Mediation practices can be done with mediation and breathing techniques to calm the low lever fear state as mentioned in the comments.

However, long term integration of the trauma, really needs to happen in a safe environment where a person can sit and listen to you and feel with you as you process the vulnerability of the trauma. This takes time and consistency.