If what you say is true:
'My department head keeps e-mailing me insulting things about how bad my attitude is and CC's the general manager of the company'
that is not only harrassment but the e-mails are proof of it.
DO NOT DELETE THOSE E-MAILS
AND
DO GET AN ATTORNEY
if you go in during lunch you can stay until dinner at which time the price goes up and you will have to leave, but, if you go in during dinner, yes, you can stay til closing.