I read 'What is Metaphysics' on the internet instead and I found it very interesting. The proof that nothingness precedes negation is very elegant although I'm still having a difficult time grasping the implications. However, like most Germans, he is a mystic under his technical incomprehensibility. I for one have never felt anxiety, and I suppose that if such a feeling was possible - even though it's rare - someone would already have talked about it before Heidegger (at the very least, he could describe the circumstances under which he felt anxiety?)