Weird memory error message

This one's new. I had a BIG post which updated just fine. Left that page open for a while in the browser (probably a long while, went to lunch). When I came back, this was displayed above the edit field in red:

Fatal error: Out of memory (allocated 9437184) (tried to allocate 6144 bytes) in C:\xampp\htdocs\wpmu-zdecade\wp-includes\deprecated.php on line 948

Ever see this before? Any idea what might cause it? Yes, I have plug-ins and such, but this was in an un-touched editing screen.