You are not alone! And you are not stupid!
What helps me sometimes was thinking of what I would do in my native language if I couldn't think of a word
--describe it (it's red...it's a fruit)
--approximate (it's like...an orange, but red)
--give the larger category (it's a bird...if I don't know "speckled grouse")
--use phrases like "it's that thing..." "it's like when"... all languages have them, you just have to figure out what they are
--use hand gestures
I listen to music in my second language if I know I'm going to have to use it. It seems if that part of my brain gets "turned on" then it works better...
Some people even get hyponotized for things that make them that nervous...as you know it's the fear that is the problem, not your knowledge!