I am 48 this year and have suffered from MECFS since 2002. 
What I miss is having strength to accomplish the things I used to be able to so such as working full time, exercising at the gym, jogging, rollerblading, and feeling refreshed after a goodnight sleep, that hasn't happened for me in decades and I do not remember how it feels not to be tired,in pain, physically weak...many times not able to get out of bed for a couple of days after I exerted myself.

Compared to a healthy person  this is not exertion, but for those who have CFS  everything a person does with regards to daily living takes energy...or having balance issues, memory problems or able to mentally focus while reading, writing letters, listening to my friends speak on the phone without becoming tired after a short period of time..I really miss living my life without daily taking medication for my illness.

I miss the person I was before I developed CFS..this illness changed my whole life.