Warning: Frustration post.

In the last 6 months I got that strange feeling that I am actually moving backwards with my Chinese abilities - with a narrower and narrower active vocab base, stagnating speech recognition, and a losing grip on Grammar. This is actually a lot worse than the usual "oh, I hit the next plateau" feeling. This "plateau" seems to have a downwards inclination.

And all this despite the fact that I didn't at all reduce my time slot - much the opposite so. I ramped it up. I inserted new sources (HSK material, exercises, 红楼梦, more Chinese with my collegue...), but it all doesn't help.

For a long time it was always moving upwards - conquering more and more territory with an almost linear builtup of vocab and grammar, seemingly getting within reach of basic fluency and a 80% listening comprehension (at least in my daydreams). But recently this all seems to blur away from the edges.

Has anybody else besides me experienced this? Is it only temporarily? Do I need different input? Should I take "real" classes?

All with the scary question in the back: Can this actually be done from outside China?