If you look for your mailbox - and it has suddenly disappeared - no worries... just go to the bottom of the page and click "Prev 50" - this will bring up the page where you will be able to locate your box!
It is customary for one to reply to those who have left you a personal message by posting your reply message in that persons mailbox - they may not be checking for an answer in your mailbox!
Just thought I would post a coupla tips you may find helpful!
Namaste... ~eerie