I felt compelled to tell just about anyone I came into contact with!
For work colleagues I tried to arm myself beforehand with knowing a bit more than I expected them to, if that makes sense. Most people knew there was something wrong and received the news with a comment along the lines of ‘Oh, sorry to hear that’ and that was it.
The most helpful comment was ‘Well I’ve heard of MS of course, but I don’t really know what it is’. I explained that I didn’t know a lot at that stage, but it is an autoimmune condition that affects my central nervous system, which in turn will cause many and varied symptoms.
I continue to use that stock response with everyone else. My employers are great, very flexible with my work hours and time off sick (just had Lemtrada so took several weeks off in August).
Tell the DVLA (if you drive) and insurance companies.
Re family - siblings are statistically slightly more likely to develop MS than other relatives, so I told them to be aware of anything unusual in their own health, and also so they could inform their GP’s if necessary. My family are very down to earth so I had no extreme reactions or panic.
I only found telling people stressful if they assumed or ‘knew’ how awful things were going to get. You will always get the odd one who catastrophizes and loves to share made-up horror stories. Or ‘helpfully’ passes on miracle cures then gets annoyed when you don’t fall at their feet in gratitude.
So, try not to stress about other people, do whatever you feel comfortable with.