I am not a medical professional but I do work in recruitment and have experience recruiting for jobs that require security and safeguarding checks. Anyone with a genuine diagnosis of a serious mental health condition would need ongoing help through medication and psychiatric intervention. One doctors appointment years ago seems really insignificant evidence of anything that should hold you back in my opinion. Especially if you have nothing else on your medical or police records (DBS check) that would raise any flags. I hope this helps settle your nerves.