The only thing I could imagine it being caused by, is low oil. I had topped off my oil a while ago and the Vtec was engaging fine. Last night though, it stopped engaging and I was getting a rev limit at 5000 rpm again. I checked the oil level when I got home and it was half way between the full mark and the low mark. I guess this is what causes it to limit my rev at 5000 rpm.

Can anyone confirm if this is true or at least possible?