I've been playing Reach fine all of today. I loaded up the game again while I popped to the toilet. When I got back, it was asking me to create a Spartan. At first I thought I hadn't been logged in but it still had my tag.
 
What the game has done is erase my Spartan design and all my campaign process only letting me start from the beginning. Not the worst thing in the world considering it is fairly short but this is still rather annoying. I still have my XP, the gear I've already bought and my records including a challenge I completed today.

So uhh... is this a known problem? What the hell happened?

Wow, that's a bitch. Hopefully you weren't near the end of a Legendary campaign run?

Wow, that's strange. Bad luck maybe? I beat the campaign on Legendary solo, I would hate to lose my save if this is some known problem.

damn

You probably fell asleep on the toilet and dreamed you played the game and gained dream credits instead.  Only possible story I can think of.

Ouch. That sucks. How far were you into the campaign?

I completed the fourth mission on Legendary today, and two hours later everything was gone. Not a good feeling.

Very strange.  I assume you tried shutting down the console and restarting it, confirming you're on xbl?

That sucks. If anyone else thinks they are having this problem, try checking all your storage devices just encase you accidentally selected the device you don't use.