[miajag81]

Kind of along similar lines to the OP:

I stopped growing for a year when I was 5. Kept eating, etc., just no growing at all for a whole year. My parents took me to several doctors because they were afraid I would be a midget or something. I eventually started growing again but had fallen behind others my age and was always very small for my age until I hit my growth spurt in 7th-8th grade.

Also, for a few months when I was 8 or 9 I inexplicably starting interchanging W's and R's, Elmer Fudd-style. My parents kept asking me if I had hit my head or something, and I was terrified that I had a brain tumor or was retarded. One day I just returned to saying W's and R's normally again.