YES. I find that I can't think properly (drawing a blank, like you mentioned) and freely the way I might if I were on my own. This limits me to saying pretty basic things. When I work up the courage to (and this is both upsetting AND infuriating while I type and think about it) speak, my explanation or whatever I'm talking about just sounds confusing, I get tongue-tied and I feel like I'm not making any sense. Then the person responds in a way that shows they totally missed what I said.
Lately I've been listening to other people's conversations to try and picture what I'd say if I were in the conversation. Most of the time I picture myself saying "yeah, that's true *nervous laugh* *overly smiley*" and then the conversation wouldn't go much further.
I HATE not being free to say what I want. When I'm away from a social situation I think "I should just ... exist. I'll say what comes to mind". But, as many of you probably experience, nothing DOES come to mind except the negative crap.
Its gotten better for me in the last few years around people that are a bit quieter than me, where if its at school we're just going to talk about school-related stuff. But when the more outgoing students are chatting about other things, I either:
1) Can't contribute because I don't keep up with pop culture (shows, music etc that are popular NOW. I'll probably like them when they're in re-runs lol)
2) I'm much too nervous and feel if I speak, I'll be unheard and embarrassed -or get tongue tied etc
3) I'm extremely sensitive to people's facial reactions
4) I'm horrible at keeping up a conversation and I HATE the feeling I get after I've kept up a 10 second conversation and it.... dies because I can't say think of anything afterwards other than "yeah" or "that's true". Ugh.
So. People at school/work never get to know the real me. I'm certainly in one of my "I hate social phobia" days. Sometimes I like it, at least it keeps me humble and non-clonelike.