Nikon FM shutter fired unintentionally

So, just got a nikon FM. Shot a roll through it and everything went on beautifully. Yesterday I dropped it accidentally (small drop) on a carpet floor. I checked it and everything seemed fine. When I pressed the depth of field preview button, though, the camera fired (shutter was cocked). I then went on and removed the film cannister inside and cocked and fired the shutter a few times (and also pressed on the depth of field preview button ocasionally to see if this would persist) but everything went back to normal. I'm a little frightened though. I'm currently throught a fresh roll of film. Has anyone been through something similar?

My guess is that the fall onto the carpet acted to almost trip the shutter due to shock on the release mechanism. Pressing the DOF preview provided enough of an internal movement that the shutter tripped.

It's also my guess that the camera is fine, but I have never experienced this.

Probably just got out of sync for a second. I've had it occur on the Nikkormat FT series bodies before. Also had it occur on an F2A, after I'd used a 7.5/5.6 Fisheye-Nikkor on the body.

-J