I had a similar problem a while back. Unfortuately I had both shoes lockedand unwilling to come out. Needlessto say I to a tumble and the stupid shoes still stayed locked in. Luckily my husband was with me at the time and I had to remove my feet from the shoes. Gerry the managed to get them out the cleats using a tool he had with him.These were spd cleats and pedals at that time. It was the same thing as yourself the cleats had lossened.
I think Gerry first loosened the tension of the pedals. Maybe is yours is adjustable you could also try that if Edens suggestion doesn't work, although it sounds like it should do the trick.

I now use Look pedals and cleats