Thanks all for the reply :
>Watch British and American movies in their original language
Yes, good idea, but most of the time actors talk very (VERY) fast...
But I'm talking about a mental blocking first.
Explanations : Sometimes (very rare), this blocking left my head (I feel it), and so I have a better english understanding, but the blocking come back after a few moment (I feel too)...
So my first goal is to remove this blocking, I'll progress in english after I think...
Any ideas ??
To a non-native speaker, native speakers always do seem to speak very fast. To me, this is especially obvious with Spanish. But that's where the subtitles come in. First, use French subtitles just to get a feel for it, then switch to English subtitles. Start with big-budget Hollywood movies. People tend to speak quite clearly in these movies. Also, I recommend the TV series Mad Men. It's very dialouge- and character-driven, but not as fast-paced as for example The West Wing.
I'm a big lover of British English but the many accents can be hard to get your head around at first. Start with something that's intended for an international audience, such as Harry Potter (yes, really).
Now, I'm in no way a psychiatrist but as for the mental blocking: To me it sounds like you're just having a slight psychosomatic manifestation of your frustration in not being as fluent as you want to be. To get rid of this blocking feeling, I still believe practice is the key.