This happened to me too! Still happening now.. In August, sudden loss of clarity at distance resulted in me needing specs for distance... 2 weeks later my sight appeared to be normal again except for reading distance. I went back for another eye test and was prescribed reading glasses and advised to see my G.P. Here I am having been diagnosed as diabetic. My sight has since changed again.. now using reading glasses for seeing everything. without them my vision is blurred. My nurse said that once my glucose levels stabilise my sight should return to normal.