If someone handed me a sick note for stress and anxiety they would jump to the head of any P45 queue.”
I would agree. If it was my first year in the job I would move heaven and earth to make sure I did the best I could, worked hard and worked through sickness if I could. That’s the sort of person I would look for if I was an employer. Work isn’t a right, someone is paying you money to do work for them so if you’re not up to it you’re going to stand out.
Stress and anxiety? Used as an excuse by loads of people who can’t get their job done or can’t be bothered to make the effort. Not all cases though.
Unfortunately in the real world you can be dismissed for many valid reasons (and no mention of the real reason) perfectly legally. I’m afraid you haven’t been discriminated against, you just haven’t been as good as the other people and you stand out as being a potential liability. Sorry, this sucks but it happens.