Placed mine on the charger, laid flat, last night around 10PM with 13% charge...woke up 7 hours later and it's only at 83%
I guess next step will be to change the wall wart and see if that makes a difference tonight
Did you try using the block and the cable that came with the Watch laying flat? Also do you happen to have any podcasts or Music syncing to the Watch lately? The syncing makes the Watch charge a lot slower than it otherwise would.