I don't usually fill an entire page of a sketchbook, but I'm pretty sure this was the result of buying a new pen...apparently a brushpen. I was fiddling with it, trying to find the various ways to use it, and in the top left corner it says "pencrazy" (upside down).
Maybe I should buy some new pens, or drag out some I haven't used in a while. It always inspires me to draw, or at least doodle. I have a glass pen with a nib like a swirly ice cream cone. You dip it in ink and it draws for a very long time. I guess it would help if I had a table just for drawing.