Lost youth, hell; I'm scratching my head wondering where late middle age went to.....
Seriously, though, Charlotte, you being hospitalized for so long at so young an age was a real tragedy. That is the time when many young people have the experiences that lay the foundation of their adult lives. It is reasonable that you should mourn it.
Just don't spend too much of your energy on it. The memories that will comfort you later on are born in the here and now. What you do in the present, right now, matters.