I personally think it's your right to share as much or as little as you wish. I don't think you "owe" it to family or friends to tell them everything, regardless of their wishes or emotional needs. When I was in medical practice, I frequently had patients share intimate personal details of their health, which they asked me not to tell their spouses. Relationships are complicated, as are health issues, and full disclosure is not always best.
Do as you feel is the best for you and your family and don't care about what other people might think.
The downside of not telling them is that they will not be able to give you support when you need some. And support from your family and friends can sometimes be a good medicine. But they should also respect those moments when you don't want to talk about your health issue or just be left alone to clear up your mind.
Unless your personal health has become public health, do as you wish.
If it's something communicable that they need to know about for their health I think that would be important info for them to have. Otherwise? It's yours to with as you wish.
Brian
Maker of Kramperts Finest Bay Rum and Frostbite
Or find it here: Italian Barber, West Coast Shaving, Barclay Crocker, The Old Town Shaving Company at Stats, Maggard Razors; Leavitt & Peirce, Harvard Square
I frequently tell patients that it is their information. However, I have seen families have more difficulty in dealing with a rapid decline since they had no idea anything, widely metastatic cancer, was going on. Then out of nowhere, the husband and father was transitioning to hospice.
From your perspective it could be a bad thing to do -- depending on a bunch of things. From the perspective of your family, however, it could have other repercussions. I think that anything that could be in any way hereditary or genetic in nature may well warrant sharing with siblings, children, etc. But in the end it's your call. If I had a life threatening disease -- like cancer -- I would probably give the benefit of the doubt to my relations. If it was something chronic, perhaps less so.