I think I may be too stupid for RPGs
I try DMing, but whenever I sit down to make an adventure my mind goes completely blank. I can't think of an adventure, I can't draw a dungeon, my brain literally refuses to work, and I end up completely bullshiting the session because my brain doesn't work
This came to a climax when I was running GURPS. None of the players had played GURPS before, and it was in a post apocalyptic setting, so it was a joke. Characters were dying left and right from gunshot wounds, combat was taking too long and was too lethal, I was forgetting rules left and right, and the game was just not fun. My players kept saying "yeah, that was fun, nothing wrong", but they would then be completely silent till the next week. I eventually just stopped
I know I'm not smart enough to do anything in life, much less play RPGs, but this is one of the few respites from my retardom. What should I do?