Shit! I think I just deleted/archived FB Messenger messages....can I get them back?

[BorntoFolk]

I'm having a very long conversation with someone via Facebook Messenger but I think I've done something weird as I can only see back as far as Tues, then at the top of the screen is his profile summary and I can't scroll back any further...like it's the beginning of the conversation!

Luckily on Facebook proper I can access all the messages but I'd really like to be able to on Messenger too. Anyone know what I've done, and how to get it back!?