Last week I could read almost every single kanji in anki no problem, was getting 90%+ with reviews. In the past three days however, it's like 60% and even words I learned months ago seem to be slipping through the net. It's like my brain is refusing to accept more vocabulary or something.

Does anyone else experience this?

Note: I'm studying Japanese 4-5 hours a day at the moment and and working along through KO2001 while importing sentences from WWWJDIC. I do feel I am going rather fast but that doesn't seem to be a problem.

Sentences on WWWJDIC are from Tanaka Corpus. Beware of massive unnatural Japanese.

Sleep, diet, attitude. Those are what do it for me. SRS exposes in quantifiable ways things we may not notice otherwise. If I didn't sleep well one night, sometimes I just skip reviews the next day because I know it's not worth it; i'll just fail a bunch and get angry. Are there factors like that for you? Maybe it's something you can control.

Also: forgetting is part of learning. If keep at it, you'll get it eventually.