IMO, based on personal experiences and research I have done, it's not the combination. It's simply the fact you abused alcohol so much in the past. Withdrawal gets worse every time you go through it and these sensitized effects are permanent.
It's called Kindling. Everytime you get drunk and go through withdrawal, your brain remembers the process and it becomes reinforced. It reacts more aggressively (down regulating GABA, up-regulating Glutamate) to the alcohol next time and once the alcohol clears, you get the effects worse and worse every time.