My third biggest fear is going blind. As someone who’s identity is shaped by my ability to comprehend and analyze complex ideas, becoming blind would destroy reading for me. Sure, it may still be possible to obtain ideas from non-visual sources, but ultimately, reading is the medium that holds the highest information density for me, since I read at around 1k words per minute.
My second biggest fear is death. As a transhumanist and an Atheist, I believe that death is the ultimate annihilation. There is no salvation. There is no afterlife.
Despair can only exist if hope exists. If we believe that death is inevitable, then death seems far less scary, because nothing is lost by dying. On the other hand, if a 25% chance of living forever exists, then death would be far more intimidating, for to die is to lose an eternity of experiences and fun. It is the slim hope of indefinite life extension that motivates me to do everything in my power to obtain it.