I've noticed the same thing...
When I'm depressed, my handwriting is small, neat print. When I'm angry, huge angry print, and when I'm hypomanic (Mine's happy), it's like a mixture of cursive and print, and looks really romantic. When the hypomania's wearing thin,and I'm agitated and irritable, it's terrible, scribbles and what not. Which leaves me to re-write, because I hate making spelling and grammatical errors as well as writing illegibly...

Strange that we all have handwriting cycles