It sounds as though you're in a fixed rather than a growth mindset - you're seeing being gifted as a property that you used to have but don't feel any more, and as something that is, or was, a property of you independent of what you do with it.
You might find it very helpful, even perhaps revelatory, to read something by Carol Dweck, such as her book Mindset. In a nutshell, she argues based on research that the growth mindset is more productive. (This is a separate question from whether it's true, which is a bit hard to get one's head around! But in any case, success in anything worthwhile certainly does require work, perseverance etc.)
Alcohol and some drugs can have damaging effects on the brain physically, and if you haven't done much that's intellectually demanding lately that also won't have helped, so although "my brain is gone" is probably over-dramatic, you could well be objectively correct in perceiving that in some ways it doesn't work as well as it once did. However, that can be temporary! The brain is remarkably plastic; you'd probably be surprised how fast you'd feel comfortable again doing whatever hard stuff you want to do, if you started working towards it systematically.
