I mean, you can always start Year 13 next September if you think your mental health might negatively impact your A-levels. I think it would be better to get grades that reflect your true abilities later and get into the university you really want, rather than end up with grades or a uni choice affected by your mental health.
I’m just not sure how this would impact your courses or predicted grades. Is your school okay with you taking a break and coming back later to finish the courses? If so, then I don’t see why not. You could use the year to recover but also to learn for fun.
I’d also say don’t make any rash decisions. Sometimes when I’m really struggling with my anxiety, I feel like throwing everything away lol, but afterwards I’m really glad I didn’t do certain things out of sadness or stress.
Do whatever you think is best, but definitely discuss it with your sixth form/college.