I also suffer from blocks. I have good days and bad days. Some days it seems I'm perfectly fluent, other days it seems like I'm having a block in every sentence. I haven't quite nailed down what causes them, but they DEFINITELY come out in high pressure situations. I have tons of blocks when I'm doing job interviews or presentations. I also have lots of blocks when I'm talking on the phone as opposed to in person. For me, it seems like my blocks mostly happen on words with vowel sounds at the beginning. For example: elevators, Allison, Evan, economy, Alabama, Impala, engineering. I'm not saying that I have blocks on those words every time, it just happens more frequently with those words over others. I wish I could give you advice to help, but I'm also looking for help, so I can't really help you there unfortunately. You're not alone though. Blocks suck.