iMessage thread just disappeared. Poof! It's gone. Help!

A long-standing iMessage thread just disappeared this morning on my iPhone 6 IOS 8.1. I had a new message from him on my locked screen and when i unlocked the phone to go into the Messages app to click into the thread to respond, the entire thread disappeared. I also had a brief difficult time getting a call to go through to his number at the same time, but that fixed itself.

Anyway. Poof! The thread is gone. Every other thread from all other contacts are still visible to me. I've started a new thread with this contact, and everything is fine, but I want the history of our conversation back! Help! Thanks for your help!