Accidentally Alt-Tabbed, now my font is tiny

[loramin]

I'm no expert, but that does look like some sort of resolution problem. First off I'd try entering/existing full-screen (it's not likely to fix anything, but it only takes two seconds and could help). Second, I'd check all of the resolution settings in eqclient.ini. It's possible you have some that are correct, but one set is off.

EDIT: Or do it in game as Tupakk suggested (posted before I saw his reply).