"I talk to myself all the time in Spanish and it sounds good to me:)" this is interesting and I do that myself too. When I speak to native speakers I often pause and think for seconds just to look for a word I already knew. I guess it's just a natural part of the process and all we should do is keep practicing! 

You are not alone) Personally, I can't talk with people who doesn't want me to talk to them - I mean unfreindly people who pretends they don't understand me. In the other situations I cope pretty good, because when you talk to your friend on italki or to the kind people outside and suddenly forget the words - your speaking partner will help you, for sure. Just take a deep breath and make a big smile)

I usually end up forgetting everything regardless of the language I'm speaking haha, I just lose all train of thought and up doing the whole blank look "duhhhhh" thing too.