Oohhh it hurts! I haven't had an earlyish 9 treasure feeling in a long time now. I didn't mean to walk onto the trap door. I saw it, but somehow before I knew what happened, bam, "you've set off a trap door!"
I resumed my game despite the sinking feeling of "what if" and it was a surprise when, later, after running out of ammo, I got myself out that very problematic situation using a potion of surprise. I will upload a video of this interesting adventure soon!