Hmmm... Just wrote my answer then saw your extra info. Okay, so it's not a blown gasket between 2 & 3 as I first suspected. If this happened all of a sudden it sounds unlikely that you just dropped two exhaust valves. (Intake valves tend to live longer lives than exhaust valves.)
Cam shaft? Hmmm... No, even that would be unlikely... heard of it but it's not a racing engine, it's a lil' civic. But it's theoretically possible that your cam's lopped a couple of nodes. Hate to imagine how but best to mention it.
But let's be realistic. Here's an idea: take off the rocker cover and do a visual check to see if the amount of movement of the valves for each cylinder seem to be the same. If they are then the cam's likely okay. If any valves on the dud cylinders are sitting a fraction wrong, then consider they've chipped/burned/pitted at the edge etc, or a seat has let go.
Not much else I can think of at the moment. Most unlikely you've burned tiny holes through the tops of two pistons, unless your car's been running awfully lean.
Let me know how you do. You can send me a message via my profile page. Really love to know what's wrong with this one.
All the best,
L.
