Hair extensions dangerous???

I was considering getting extensions recently (As you can see by my Hair Extensions and girliness topic in Hair politics) and now I'm quite scared.

Your own hair might fall out??? You can't actually grow your own hair out because the extensions damage it?

My image of extensions were something that you get put into your hair almost semelssy and lasts at least 6 to 8 months before falling out or anything.

I don't know now.