It's actually not the wormwood that gives you the hangover. It's the combination of the alcohol and the wormwood. To avoid this problem people will often make it in really strong hard liquor and burn off the alcohol. That's why they add the sugar cubes to it. Wormwood is bitter plus the...
When i do one gallon batches the yeast usually eats up the sugar within a week. You definitely need to back sweeten or you'll be left with what taste like an unripened green apple. Or in my case, pure stomach bile.