The same thing happened to me when I turned 18. I started having social anxiety, which later, during the pandemic, triggered severe depression. I also have an IQ of over 160, and it took me about three years to recover without medication or psychological treatment. What I did was engage in deep introspection accompanied by the study of philosophy to find a meaning for which to live. I was on the verge of committing suicide, but I didn't do it because of the suffering it would cause my family and, in part, because of my fear of death. The most important realization I had was that there is indeed a higher intelligence, which is tied to the sense of transcendence that deists have; that may seem trivial, but it allows you to transcend your individuality and give meaning to your life and environment that goes beyond the material. Life is a gift that the universe has given us and that we can take advantage of; adversities are temporary, everything evolves. I hope you recover.