I have had a CS on mental health grounds for anxiety. Despite this, they would not have done it before 39 weeks (I was booked in for 39 weeks) unless there was a serious medical reason (which includes mental health) for doing so as there are more risks to the baby with regard to breathing.
For them to bring forward your date, this close to your booked in date, they would have be believe that you were at serious risk of something happening to you or your baby. To put it bluntly, you were at risk of harming yourself unless there was a physical need to carry out a CS earlier. If this is the case, then you need to be going to the hospital and telling them that you need emergency help, in order to get the proper mental health support you need. The chances are, you'd probably find in those circumstances they would still be unlikely to carry out the CS then and there and would be more likely to admit you as a mental health patient and still carry out the CS on your booked date.
TBH, I'm not sure that when you have the CS is really your issue here. If you are struggling in the way you are now, having the baby a few days earlier is not going to resolve the issue. Its just that the baby arriving proves a focal point for all the stresses and strain you are under now. The babies arrival isn't necessarily going to be the end of that, and may indeed compound problems.
You do need to talk to someone. Share how you are feeling with your family. Even if they do have stresses of their own, they need to know.
Chase up with a midwife about the mental health thing tomorrow.
Make sure they are aware that you have been really struggling this week when you go in, so they can keep an eye on you and maybe chase up / make you more of a priority with that mental health appointment if the midwife has not already done so.
Hang in there.