
Candida albicans can cause severe life-threatening infections, usually
in people who are otherwise quite ill.  This is not, however, the sort
of illness that you are probably discussing.

"Systemic yeast syndrome" where the body is allergic to
yeast is considered a quack diagnosis by mainstream medicine.  There
is a book "The Yeast Connection" which talks about this "illness".

There is no convincing evidence that such a disease exists.