Oh, that poor baby! Obviously, SOMETHING scared him....or he could just be afraid of being without you again. Maybe he was scared since he was gone for awhile (30 minutes probably seems alot longer to them than it does to us) - I really don't know
Maybe a grumpy, angry cat came up to him and hissed or pawed at him and it freaked him out?
Or maybe a bigger dog somehow scared him? Who knows....but I hope that with time you have your "old" Tank back!
