Will I be restricted from health care?

My current insurance is United Healthcare. About a year ago I went on cobra but still maintained united healthcare. This year my Dad changed jobs and the took the new insurance policy at his current company which also United Healthcare, both policies from his last job and current are good. Also I am leaving cobra since iI have already been accepted on his plan but I'm a little confused. not once was I without insurance from United healthcare, it's just the policies are different because my dad moved from one company to a next. I got an email from some healthcare care company asking to do a medical exam on my email and now I'm freaked out, the company is American para professional serv. But hey don't give me much info just that my application for insurance was received, but I already got the card for the new policie weeks ago!. Not once did I leave united healthcare! I have been a little sick and the doctors are still trying to figure out what's wrong with me. Can I be denied coverage even though I have been insured with United Healthcare since 2008?