Efudex side-effects

Hi, I was prescribed Efudex 5% for a place on my thigh and found this discussion site when researching info about possible side-effects.  I started using it 1 week ago and the only thing I've experienced is trouble sleeping. My lesion is only dime-sized and I was wondering if I am going to suffer the effects people have described on this board. My doctor never told me that if the spot was skin cancer or not. Is the fact that he prescribed Efudex confirming my fear that it is? I called his office asking for a sleeping pill prescription and was told they would call me back. (which never happened). Any replies are welcome.