Great observation. I would stop trying to get through the brick wall. It only fuels the block. Just wait it out. Eventually it will pass. It has to. Otherwise you would be on constant blocking state. Then, when the "brick wall" dissapear, try to speak. I'm currently reading a book that talks about this. The author said is all about states. If there´s a blocking state there is a fluency state too. If you are alone and speaking just fine it is because you are on your fluency state. The trick is to indentify both states and try to move from one to the other. With time and practice, you will feel the blocking state coming and rapidly replace it with the fluency one avoiding the block.