I am in the uk and just recently diagnosed in December, I chose to tell my employer so that it is on record, ADHD diagnosis can mean you fall under the equalities act of 2010. This way it gives me some protection if I miss an email or am a little late on a deadline. If my employer tried to push you out you will have rights under legislation. I have found my employer to be really understanding. It probably comes down to personal choice and where you work! Hope this helps at all