Immediately begin preparing what I need to live. Albeit I might want to kill myself in the end, it's not smart to be making rash choices right away. Work on the basis you're not alone, work on the basis you want to live, and go from there. If I end up going insane and killing myself, so be it.
Remember; Who will operate, maintain and manage all the Water, Electric & Gas supplies? No-one, so get ready to go full Zombie Apocalypse mode. I Am Legend mode!