Will a retainer make my teeth fall out if..?

If I haven't been to a dentist in a few years.. I lost dental insurance so I haven't been but I do brush regularly and they don't hurt and they are pearly white but since they haven't been checked in a long time I'm worried they might be unhealthy.. I got invisalign two days ago and my teeth feel very loose! Will they fall out since I'm not sure if they are completely healthy? Should I not wear the retainer? Also its tight and kinda difficult to remove is that a problem? I'm scared my teeth will come out with it lol