The same thing ALMOST happened to me, yesterday. I have my Westy 12 clone in the primary. Didn't see any activity yesterday morning, but by the time I got home, last night, the kreusen came up, and subsided in 12 hours. It came up and just barely touched the bottom of the airlock. Fortunate for me. I have it sitting in the empty dining room, on a beer case, on my newly refinished oak floors !!!!! Could have been a disaster, not to mention how pi$$ed off I would have been, for maybe ruining the floor.
Anyway, that does happen, I will definitely NOT have the next batch where this one is fermenting. At least I'll get it set in a tote, or just use a blowoff tube. I'll have to get it dog proofed though. A 100 pound Chessy does whatever he wants to do. LOL