Stuck, again

Sometimes I feel like I get so stuck in Chinese. I can't communicate with people. When I try and say something, I become mute or say incoherent things. I feel like others can't understand me, regardless of whether they can or not, and I'm not able to use different words and grammar that I do know to explain myself. It's hard to tell if the problem is that I'm just realizing that I want to say more than I can and can't figure out how to simplify, or that I'm overwhelmed by the fact that there's so much that I don't know in general, or that it's an off-day (/week) so things that I do know aren't coming to mind. In any case, it's frustrating. Usually when this happens, motivation factor kicks into high gear, because I have a strong need to feel like I can communicate. When I'm studying, I'm more confident, I remember the things that I have studied, and do a better job at using simpler grammar and vocab to communicate. Time always helps, too, in getting over the language hill.