I think it's part of the whole detox process to have rampant fear. That didn't subside for me for at least a couple weeks. Then it took another several months for the general anxiety to ease.
Keep reading here on this site, there is a deep well of wisdom here from addiction to mental health. Since you have meds, take them as prescribed and try to be gentle with yourself. If you were honest with your doctor, the meds will do the work of keeping you safe from the dangerous parts of withdrawal.