What was the mishap that made Helen Keller lose her facilities of seeing and hearing in The Story of My Life?

Helen got an illness when she was about a year old that left her blind and deaf.

Helen started life as a normal baby.  She walked at one year old.  She was very intelligent.  However, when she was nineteen months old, she contracted a terrible illness.  She recovered, but with a tragic loss of senses.

Then, in the dreary month of February, came the illness which closed my eyes and ears and plunged me into the unconsciousness of a new-born baby. They called it acute congestion of the stomach and brain. The doctor thought I could not live.  (Ch. 1)

The exact illness is not specified, but doctors called it “acute congestion of the stomach and brain.”  They did not expect Helen to live.  She was in great pain.  She recovered, but her intellectual growth was stagnated by the fact that she could no longer hear or see.  It is hard to learn language when you can’t hear.  Helen had not been talking much yet since she wasn’t even two years old.  She had to learn to make do.

My hands felt every object and observed every motion, and in this way I learned to know many things. Soon I felt the need of some communication with others and began to make crude signs. (Ch. 2)

Poor little Helen tried to communicate with her parents, and they did their best to accommodate her needs.  It became clear that something more would have to be done.  This was a case for experts.  Since there was no school for the blind and deaf nearby, her parents sent for a teacher. 

Anne Sullivan was able to teach Helen how to speak, read, and write.  She taught her sign language by spelling into her hand.  Helen’s first word was “water” and she blossomed from there. Her intelligence made her a good student, although she could also be stubborn.  She came to love and rely on Anne.