Why the Two Conditions Feed Each Other
Say drinking calms your anxiety at night. It works, at first. The tension drops and you finally sleep. So you do it again the next night, and the next.
Here is what happens underneath. Alcohol changes how your brain handles stress. Over time it makes your anxiety worse, not better. You wake up more on edge than before. So you reach for the drink earlier. The thing that quieted the symptom is now fueling it.
This loop runs the same way with depression and trauma. You use something to numb what hurts. The relief is real but short. Then the use adds its own damage: missed work, strained relationships, money problems, worse sleep. Those consequences deepen the depression or the fear. And the deeper it goes, the more reason you have to use again.
Round and round. That is why treating only one side rarely holds. Get sober without addressing the anxiety, and the anxiety pushes you back. Treat the depression while active use continues, and the substance keeps undercutting the progress.
One point matters here. Neither condition simply caused the other. Your anxiety did not make you an addict. The substance did not plant the trauma. Both are real medical problems, tangled together. Good treatment works on both at the same time, because that is the only way to break the cycle.