There are many reasons to blog: keeping in touch with friends, sharing your expertise, publishing your own stories without waiting for the publishing world’s permission, or chronicling your own journey, whether metaphorical or geographical.
Those fighting chronic illnesses have many compelling reasons to blog. They can trace their reactions to different treatments, get their feelings out and deal with them more effectively (the pressures of not wanting to burden other people can be a huge stressor in and of themselves), and keep in touch with people when they may not feel like having company over. Blog circles and services that deal specifically with patients can be comfortable environments where bloggers feel safe and understood in ways they might not be in the blogosphere at large.
To find bloggers dealing with the same issues as you, surf the Tag Pages for Cancer, Diabetes, Heart Disease, etc, or investigate services such as TheStatus.com, which offers secure, encrypted pages to ensure privacy. Carepages.com is a similar site, although friendlier and more social. Be careful to read the Terms of Service wherever you’re thinking of signing up. MyCancerPlace.com is a similar kind of site for cancer patients, but it takes the copyright for everything that you write or post. This is not, in my opinion, acceptable practice. Be aware, and if you’re blogging on behalf of someone else, be very protective of their rights.
That’s another point: some treatments and illnesses interfere with the patient’s ability to blog for themselves, or to read complicated material. If you know someone in this situation, you can offer to do the setup for them, taking a seemingly enormous load off them, and easing their way into blogging. You could even blog for them, like taking an oral history, or record them and upload the audio. There are many ways to help people connect with those who have shared similar experiences.