I've never seen/heard of such a thing. If my screen did that, I would
immediate suspect a virus or a bad practical joke. I don't know how to scan
for the latter, but I would certainly update my a/v software and scan for
the former. After that, I would suspect a bad video driver.
After that... I'd wonder if perhaps you a) use Word for editing email, and
b) have reset Word's default alignment formatting to vertically centering
text. Choose File - Page Setup - Layout tab, and see if Vertical Alignment
is set to Center. If it is, set it to Top, and click the Default button at
the bottom of the dialog box.