David,
Trial and error is the best teacher. Not there, so I don't know exactly what you did. How many lit coals did you start out with? Read in your earlier post that you put the meat on at a 225 temp. It's best if you use the MM to put on your meat after you add your lit coals. Or at least I think so.
You are right. The white coals should be on top. But, how good is your light source? Possibly, when you were playing with the wood chunks as you earlier mentioned, you moved some of the lit coals down. But, maybe, you are not seeing things as they really are if your light is not good enough.
Next time, trust the MM and don't mess with the fire. Not being critical. But my advice does not help you any in your currant situation!
Quit playing with your fire. Try to stabilize your temp by adjusting your bottom vents in 30 min increments. Fight the feeling to try to make it happen right now. If your temp gets too high play with the top vent. If you can't get it back up to temp, you might need to add some more lit coals from your chimney.
Again, fight the feeling to make it happen right now. Do everything in 30 min increments. Believe me. All is not lost. You may just have to forgo your snooze this time during your smoke.
Mike