Urea cream is usually used to soften and remove rough skin or to break down hardened tissue like on your toes or feet. It can cause several layers of skin to slough off if left on very long. If you already had high levels of urea in your blood, it could have caused elevated systemic urea levels which can cause nerve pain. Might want to have the doc check your urea levels as this is a recognized biomarker for long Covid.