I did 3 years of nurse training before the days of nursing degrees, and loathed every minute.
But once qualified,it opened up a whole range of opportunities. I had 6 months staffing on a ward with some really fun colleagues (much different to when I was a student), and then branched out into public health and ultimately, child psychotherapy - which I loved. The point being that without that nursing qualification, I would have gone nowhere but back onto the dole (I was 2 years unemployed before starting training. That was grim).
However, this does not mean that you should just ignore your feelings now. No qualification is worth ruining your physical or mental health. As has been suggested, speak with your tutors and see if you can work out a plan to cope with what you are finding hard. If you are consistently failing essays, that is something that a tutor should be able to help you with; if you need some strategies for coping with stress or low mood, get some pastoral help. Whatever you decide to do in the end, those people are there to help, please use them. That way, if you do decide to leave, you will know that you did your best and that you haven't failed - it's simply that nursing isn't suited to you.