IRS problem

I have been an expat for the past 5 years and have not filed a return. According to the returns that I have had prepared, I owe no taxes. I dont know if the IRS has looked for me during the past five years or not. I have been told that if they have, I could be in legal trouble for not filing the returns. I am also a Gulf War veteran that suffers from chronic fatigue, skin disorders, lapses in memory and inability to concentrate. I was wondering if the IRS will take these medical conditions into account if they are considering prosecuting me? Any advice would really be appreciated.

Thanks,

Bill